I use one alternating between a Salli and an Ikea Markus. The greatest benefit to me is in greatly improved blood flow in legs and pelvis area. The second benefit is in providing natural temperature control in an area that counts. The third benefit is in making my core muscles work.

You still can slouch in the saddle especially if you don't have an elbow support or if your table is not tall enough. If your arms are not in a symmetrical position during the day, e.g. if you are a frequent mouse user, spine would tend to curve to the side of the hand that is further from the center. This can result in scoliosis.

Would I recommend one? Yes, if you have blood flow problems.

I noticed that if I'm doing exercises I can seat on whatever comfortably save for the bloodflow issue.