Good product. Once you get it perfectly aligned it works great

I received a new 4th. Axis from the seller, and this one works fine!...Kudos to the seller for sending me a new one even when I was out of the Amazon's return window.

After I opened the box and manually tested it I realized that the new one was able to spin without much effort, opposite to the first one I got that it was hard to rotate, but since I didn't know what to expect I thought it was fine and hard to rotate due to the stepper motor (I didn't remove it). So here is my recommendation if you get one of these:
Recommendation
Once you receive your package, unscrew and remove the stepper motor (completely), as if you were trying to adjust the belt tension; this shouldn't void your warranty as you should be able to adjust the belt any time and this is not opening the spindle. Now and without the stepper motor, manually rotate the spindle/chuck; the spindle/chuck should rotate freely, without much effort but not as a skateboard wheel; great if does. Even if you feel a small amount of friction it should be fine as it should be normal on these spindles/chucks. If you have a hard time rotating it (and hear something like a clicking sound) then you should be considering exchange it.
Hope this helps.

Note: I'm leaving my original comment below in case you were following"¦

Original Comment:
Disappointed!...The spindle it's barely turning and seemed to got stuck only after a few times using it. this happened right after my Amazon return window expired, so I contacted the seller for diagrams to see if I could open it and do some clean up or add grease, but they do not have any. The seller suggested to "hammer the inside four claws from the front to the back" but that seems radical and I'm not certain it will not damage completely the spindle. I have seen videos of other 4th axis that they have retainers/big nuts that you unscrew to open the interior, but this model has none; not in the back or in the front, and I have not found a site or video that shows how to open any of these models. Do not recommend.

UPDATE 10/9/2019
The seller contacted me again and as there are no schematics available, then it's willing to help me solve the issue in a different way; by sending me a new product for testing and review, and have expedited the shipment. I'll provide new comments an possible update the overall rating once I have tested and reviewed the new product.

Running this on a G0704 conversion with Centroid Acorn driving it. No issues, it's a solid unit and price is good.

I saw a review that said there were no instructions. If you don't know how to calibrate and install a stepper motor on Mach3 or whatever, you need to do some research. 6:1 is all that is needed. The synchronous four jaw check is great for center square stock.

This uses the same spindle as my lathe and I am amazed at how accurate the 4th axis is. I have less than .0002" runout. The belt and motor are tight with less than .05 degress of backlash. Awesome for cutting gears.