I work and study in IT, so most of my work are in front of a Computer Desk, I have found this a good addition to my room and it helps me keep my back straight.
Something which I find really cool about this foot rest is that you do not need to get up from your chair to change the angle of the footrest, you can easily hit the unlock button with your foot, adjust the angle and lock it again, BRILLIANT!
It also has a non-slip surface and the size of this thing is big enough.
If I had to find something which is not that great is the price, because you can find cheaper, similar products, but it's definitely worth it, and I would recommend it.