I have been a fan of the Elecom Huge trackball for years, I found it to be best replacement for the MS Trackball Explorer from years past, though it was a completely different design. When I saw this trackball, it reminded me so much of the original Trackball Explorer that I had to give it a try. This review will mostly be comparing it to the Elecom Huge.

Buttons: While I love the Elecom Huge, it's not really designed for smaller hands like mine. The left button on the Huge is a bit too far away for my thumb to reach comfortably, so I have had to swap the Forward and Left buttons in the software, not a big deal as it's easy to do, but it's an out-of-the-box ergonomic drawback. The left button on the Nulea is more "flared" out, so it's much easier to reach with my thumb (by pressing "downward" instead of "inward") and therefore requires no re-mapping of buttons.
Which brings up another important difference: you cannot re-program any of the buttons on the Nulea, fortunately, the buttons are laid out in a familiar pattern that is easy to learn, but could be a showstopper if you don't like the current button assignments and don't want to mess with third-party utilities.
The Elecom also comes with 3 extra programmable buttons and can do horizontal scrolling, which the Nulea is incapable of doing.

Ergonomics: The Elecom has a flatter design with a nice soft rest for your palm and the huge ball makes moving across a 4K monitor screen a breeze as it doesn't require much rolling effort to go from one side of the screen to the other. The Nulea has a more raised design, and while it lacks the soft palm rest of the Elecom, it's still quite comfortable. The Nulea has a smaller ball, so there is more noticeable rolling to get around the screen, what i could do in one smooth motion with the Elecom, requires a little extra afterward to get there on the Nulea even at the highest DPI setting, so i had to adjust the pointer speed in Widows to compensate.

Battery life: The Elecom Huge can go for months at a time between battery changes, but does require physical batteries. I haven't owned the Nulea long enough to know how long it lasts on a charge, but it uses a rechargeable battery (and USB-C), and you can continue to use it while it's recharging, so that's a plus.

Overall: So far I would say if you want a programmable, feature rich trackball, go for the Elecom Huge. If you want a nice comfortable trackball reminiscent of the old MS Trackball Explorer with no bells and whistles, then go for the Nulea.

The Nulea M505 clearly took "inspiration" from the Sanwa Gravi finger ball -- word on the street is they are made in the same factory to similar specs -- yet there is enough small changes to make them different. And I think that's exactly the point, to make them different.

Tl;dr: ergonomic contour mostly the same (which is good), physical buttons arranged differently and with different characteristics (slightly worse than the Gravi for my own use but may be preferable for other people)

In terms of overall shape and contour, the Nulea M505 and the Sanwa Gravi are almost identical -- the only, superficial, difference being the front on the Nulea is more rounded. You'll never feel (or even see) that while using it. This similarity is a good thing, because IMO Sanwa Gravi is the first trackball in the last decade to actually nail the ergonomics of palm contour (more details on my longer review on the Sanwa Gravi page).

The physical buttons on the M505 _are_ arranged differently and have different characteristics. It used the more traditional arrangement where on the thumb cluster you get left button, wheel, forward, and backward. The right button is moved to the right of the ball under the ring/pinky finger. On the Gravi, you would have the right button taking the place of the forward _and_ the backward buttons, and have forward and backward as two big(ger) buttons under ring and pinky. I slightly prefer the arrangement on the M505 because it's more in line with other finger balls and is therefore more intuitive.

A big difference in terms of implementation, however, is that the left button on the M505 is slightly recessed from the casing. For people with longer thumb (like myself), this may be a problem because you'll have to curl up your thumb a bit to engage the left click -- or rotate the trackball body clockwise so your thumb lands closer to the rear end. In my opinion, neither solution is ideal because this is unnecessary restriction on ergonomics. As a comparison, the left button on the Gravi is slightly _raised_ from the casing, making it more comfortable to engage with any part of your thumb (even the joint, if you like). This may be the most serious issue people should consider when choosing between the two.

Another difference, not as big but still could be significant, is that on the M505, the upper edge of the left button sits lower than on the Gravi. This is because on the M505, the wheel is implemented as blocking off a whole stripe of real estate on the thumb cluster (the left button does not share any edge with the back/forward combo). On the Gravi, the left and the right buttons (the right taking the place of the back/forward on the M505) share a horizontal edge, and the wheel is implemented as a thin cutout on their shared edge. What this means in practice, is that on the Gravi, you can engage the left button on a vertically higher position (near the edge it shares with the right button), which is closer to your palm, and so requires less of a clawing gesture for left click than on the M505. I'm not sure whether or not this may lead to more stress on the thumb long term.

A side effect of having the back/forward on the M505 on the thumb is that the back button is more difficult to reach. Clearly not enough thought was given when the decision was made to simply split the right button on the Gravi into two equal halves of back and forward on the M505. In my opinion both buttons should be moved more toward the front.

Yet another difference: on the M505, middle click can be activated by tilting the wheel downward. On the Gravi, it is activated by flipping the wheel upward. I don't have a preference one way or another but would note that both are more ergonomic than on a typical wheel where you'll need to press inward and could accidentally trigger a scroll event.

The ball movement is appreciably smoother than the Gravi out of the box. Combining with the fact that it's also easier to remove the ball from the M505, I would guess they reduced the height of the bearings slightly.

The placement and labeling of the dpi/connectivity switches on the bottom is significantly better on the M505 than on the Gravi (The latter has the most illogical arrangement I've ever seen, and with no labeling whatsoever on 2 out of the 3 switches)

All things considered, I think the M505 is a very decent finger ball. My main beef with it is the recessed left button, which to me is a not-insignificant ergonomic regression, and to a lesser degree the wasted real estate around the wheel, which could have been used for a more ergonomic left button. But these may not be much of an issue without comparison to the Gravi. The price point of the M505 -- being close to half of that of the Gravi -- is certainly much more reasonable.

If you have ever had a many years old Microsoft Explorer trackball mouse, and wish you could get one again, Here it is.
My old trackball still works, but slowly. I wanted the same configuration and ease of use that I had with it. I found it and it is wireless, and at a reasonable price, I haven't had it long enough to address how long a single charge lasts. Set up was only a few minutes. Less time than unpacking the device. I've tried the trackball mice that have the ball at the thumb side and they are not as intuitive, nor as comfortable. If you've ever had carpal tunnel issues, or surgery, this is a very comfortable position. In the Photo the Microsoft trackball is the well worn grey one on the left.

Found this to have more features and be of higher quality than most of the other options at the same price. I've especially appreciated the decent sensor used in it, as it doesn't lose track when the ball is spun really fast. Which is a problem I've found with some of Logitech, Elcom, and Kensington's (more expensive) trackballs which may use older sensors. Moving the ball itself also feels very smooth with very low stiction (amount of force needed for small, pixel-precise movements), and I have personally gamed with it just fine. Build-wise the mouse has a similar design to other trackballs such as the Microsoft Explorer and Ploopy, the plastic also has a matte finish that feels surprisingly soft and pleasant in the hand, although as some other reviews have stated, makes it susceptible to degrade with age and use, so keep that in mind if that bothers you. The switches themselves also feel great, including the back and forward buttons (not spongy nor hard to press as in many regular mice). Although I don't know how involved the repair process could be if necessary as I haven't disassembled it.

My only gripe with the product is the length of the left click button, unless I position my hand further back, my thumb will slightly go over the edge of the front of the button so that only the middle of it can press down, while it seems like there is enough room on the chassis for them to have made a longer button. This is my only pet peeve with the device, but you may have a similar experience if you have a long thumb. Overall it provides a smooth, comfortable experience useful for both gaming and multi-monitor work spaces. Would highly recommend this product for those new to trackballs as well.

In terms of functionality, this is an excellent trackball mouse, especially for the price. The ball itself is smooth and accurate, the buttons are in the right place, and the soft rubber coating makes it comfortable to use for extended periods.

The issue with that coating is that it seems to pick up oil quickly. I've used it on and off for just a couple of weeks, and as you can see in the attached picture, it's already starting to look a bit oily (similar to what you get if using cheap ABS keycaps). So far, it's purely aesthetic and not a dealbreaker for me, but it does make me a little concerned for the long-term durability of the mouse.

Also, if you're planning on using this via Bluetooth without the dongle (which is included, to be clear), you may have to watch out for interference with other wireless devices, as I found movement to be a bit jumpy when used via Bluetooth together with a wireless keyboard and headset. The dongle clears up the issue, but it's worth mentioning in case you can't or don't want to use the dongle.