I just bought my 2nd Hyken chair. Every chair I purchased before the Hyken and there have been a few had foam or whatever to sit on and the foam would flatten out and the chair became hard to sit on. The mesh on the Hyken never gets hard and has some give so it stays comfortable. But in time the mesh failed and I had to replace the chair. But the Hyken chair was more comfortable to sit on because of the design. Even with the mesh partly failed its still more comfortable than sitting on flattened foam mounted on some kind of board. I did purchase the warranty which was a good idea it turned out. And regarding the 'fit' of the chair well go to the store and sit in it before purchasing. I am not 6 foot so this chair size is fine for me.
The seat and back are comfortable but I found that the arms were awkwardly high even when adjusted to their lowest position -- I'm 5'10". I'm now using the chair with the arms removed which is less than ideal.