Just wanted to share my failed experiment with the so-called kneeling chairs. They are designed for people with back problems. Most of your weight is transferred to your knees, with only a small amount of weight on what should be your lower back region.
I had two of these flown from Amazon, one for my office and one for my house. Great in theory; not so great in reality. Turns out the portion of the lower back that supported just a small amount of my weight put pressure just at the wrong spot and caused just about as much pain as any other chair.
I found it very difficult to get comfortable on these chairs even on good days, and would not recommend them.