Do not run for long periods.
Only used a couple of times and it no longer works.  Recently, I was shaking the 4th bottle of polish and the machine stopped and hasn't worked since.  I did notice a NOTE on the box that says: Do not run for long periods, which I'm guessing is the reason why it no longer works.  There were no instructions but I did fail to read the NOTE on the box.  Very disappointed.
Rating: 2 stars