I have the posture fit on my Aeron. Much better than the old lumbar football. I vary its position day to day or sometimes multiple times a day. The Mirra looks decent, but so does Humanscale's Freedom. If I had to swap the Aeron for a different product, it would probably be the Freedom with the high back.

Some ofthe problems I have with all chairs is simply training myself to sit properly, so any help the chair can offer me in that regard is a big help. After long periods I find I end up shifting around so that I'm not fully making use of what the chair has to offer in the comfort and ergonomics department. At the same time probably not doing my back any favours. Because of this I value being able to make a lot of adjustments to the seating so I can vary posture and tweak things for both different tasks and different times of day (depending on how slouchy I find mysef becoming). If you work in a home office as I do, don't underestimate the importance of wearing shoes. It makes sitting in any chair potentially a lot more comfortable because when you put your feet on the ground they won't slowly slide out away from you (if you have a tendancy to do that sort of thing).

Bruno