the tilt lock does not lock nor the head rest stays still. I feel like I purchased a faulty chair that did not support its key features . It is comfortable and moves smoothly on top of a plastic computer desk mat. I am 5'8 so it supports my height.
I chose this chair because it fit my 6'5" 260 pound frame (35 inch inseam). So far it has performed flawlessly but only time will tell if it holds up (I have only had the chair for about 4 months). My chair at work is a Herman Miller and since I cannot afford a Herman Miller I chose to find something similar at a lower cost and this one fit the bill for me. Being tall makes getting a comfortable chair somewhat difficult and limits choice but this one is definitely for a larger person like myself; I think a smaller person would not like this chair because it is wider and taller than most. For example my wife of 5 foot "swims" in this chair even though she finds it somewhat comfortable (her head hits the frame at the top of the chair). I would say that if you are taller than me or a long torso this chair would probably not work since I have the headrest set to max height for me but it would be fine if a person has a wider frame than me because this chair is even too wide for me (there is a LOT of room side to side between the arms - seat width is just about wide enough for me). I find the chair comfortable enough to sit for up to 2+ hours without getting up (I generally don't sit for any longer than that at any given time); and it is comfortable enough to complete my work day which can be up to 10 hours on some days. Hope this helps others make their decision.
I've only had the chair for a week but so far it's meet my expectations which were high. This is a replacement for my office chair I took home when my office closed. The chair it replaced cost $900 when purchased new. This chair is far more comfortable and ergonomic. I work for a tech company and commonly have 10-14 hour days this chair has been far better than my previous ergonomic chair. I recommend giving it a try.