I've used one of these as my desk chair for 10 years, and have had clients who have also successfully used them. I believe that a well-designed kneeling chair, used properly, can be helpful. Both are important. My chair is made by the Swedish Balans company, one of the originators of these designs. They got the design right, I think, and many of the cheaper knock-offs didn't.
Proper use is critical.
If you listen and respond to that suggestion, it can help. If you try to ignore the suggestion and maintain your habitual way of doing things, it may only become an additional source of stress. This was brought home to me by a client with a low back problem, who told me he had used one of these chairs and it made his back worse. He was tightening against the chair's suggestion to sit more erect, further stressing his back. Once he learned to relax and allow his back to respond appropriatelly, he could use the chair comfortably.