I grew up with a kneeling chair and was disappointed that they are so hard to find.  I purchased two of them - one for home and one for the office.  I use the one in the office for the entire time and everybody is complementing me on a great posture.  The chairs are easy to use and very comfortable. One of the chairs' foam is not properly fitting to cover the edges on the knee platform so I sometimes hit it with my leg.  But it is something that I will have fixed at the upholstery store, no big deal. 

Pros: comfortable. 
Cons: none.