First, the thumb rest is awkwardly placed. It doesn't go back far enough and is far too high to make the side buttons useful. This leaves you with only using the 3 keys on top, which would be ok, if the driver wasn't garbage. Previously, the driver/program would constantly forget your key assignments if it wasn't standard right-click, left-click, etc. If you program it to anything else like Pg Dn, it forgets it so you constantly have to reset it, especially after computer sleeps. Then you have to reboot for it to take effect which is incredibly annyoying when you're in the midst of work. The latest driver is completely useless and crashes the computer. The settings stick with the new one but the whole driver just crashes multiple times a day lol. I previously had a mouse driver from another company that was great, never had issues but it can't read the 3rd top button on the Unimouse so I can't use it. Super frustrating to have wasted money on this.
If you only need the right and left click with no other button configurations and you have very large hands, this may work well for you.

EDIT: I have added extra edits to my comments after 2 years of usage

Please solve these problems. You're on a goldmine and you're not capitalizing on it.

Due to hand pain after 20 years of mouse abuse and competitive gaming, I've had to look for a vertical mouse option that has a good sensor. This mouse seems to be literally the only option. I did try the Evoluent 4 out of desperation, but the sensor was unusably bad.

The thumb buttons on this mouse are essentially inaccessible for two different reasons. It's uncomfortable raising your thumb over the thumb-grip lip, and not only that, but the actual thumb buttons are way further back than any other mouse I've ever touched. The forward-most thumb button is further back than most rear thumb buttons. EDIT: I have gotten used to them in general windows usage, but for gaming they are still useless. I suggest adding two extra buttons for the pointer finger to push, like those found on the Roccat Leadr or the Steelseries Rival 500. I think these are better than thumb buttons anyway.

The scroll wheel is somewhat loose. Some other mice have a better balance on the pressure. Additionally, the actual mouse buttons themselves are not parallel with your fingers. Your fingers rest on the mouse diagonally perpendicular to the mouse buttons, so if you scroll with your middle finger, your middle finger will now be further away from the wheel than usual. EDIT: With a very relaxed claw grip I have somewhat negated this downside, but it's still a downside if full-palming the mouse during gaming.

If you don't fully palm grip the mouse, your fingertips will be further back on the mouse buttons meaning the buttons will require a greater force to actuate, meaning every middle or right click will move the entire mouse. EDIT: With 2 years of usage I have mostly negated this, but it requires extra force from your thumb & wrist to maintain stability. I have not played FPS games with the mouse however.

If you want to play low-sens fps with lots of fast sweeps while keeping the mouse fully raised, you'll have to literally apply force downwards with your thumb or the mouse will flip onto its side. I don't think this is a solvable problem with the nature of the mouse. EDIT: It's probably a little more solvable with long-term usage than I thought but it's still a downside

To say some good things, the sensor is very good. The comfort is roughly equal to the evoluent 4. The position customization is novel. The software is good. The 10 dpi steps ensure that you will find what you need.

Please make a revised version that fixes these problems and change the branding to not look and sound like a $10 office mouse. There is a void in the gaming/office community for those with hand pain, and this mouse is too flawed to solve our problems.

I really liked being able to tweak the angle of the mouse and the thumb rest. My problem is that they are tension based. The mouse angle is pretty strong so it's not easy to accidentally move. The thumb rest however moves a bit easier, and I find that I tend to rotate it while playing games where I am picking up the entire mouse more often. So it's great that you can adjust this to your exact liking, but it sucks that there no mechanic to keep it locked in place. It's like having your car seat adjusted perfectly, then having to tweak it every so often because it moves as you drive.

Defaulting the traditional right click to middle click was a massive mistake imo. Luckily you can change this. You can even change it without software which is cool, but you can't change the third mouse click without the software. The software is inconsistent across OSes. It works pretty well on Windows and has a lot of options for binding buttons. On Mac the options are more limited. For instance I cannot bind the third mouse click to forward/backward buttons.

Because the thumb buttons aren't on the rest, its almost impossible to pick up the mouse and press the buttons at the same time (like if your push to talk is bound to a mouse button). Another gaming oriented issue.

Again, a very cool mouse, but some of the flaws make it hard for me to own.

Great to avoid any tendinitis in the wrist.

I have searched for a comfortable mouse for a long time. This has been a lifesaver. I now have less hand pain using this mouse and keyboard.