I'm an exercise physiologist who specialized in Fall Prevention (balance and mobility). We use dynadiscs, (expensive version) in our FallProof class extensively. I bought one for my 95 year old mother and suggested she use it while she eats breakfast. I don't think I would recommend sitting on one of these for many hours. OUr classes run for 1 hour and we do many things in the class besides exercising while we are on the dyna disc.
More importantly than this piece of equipment is to set your chair and table height correctly. If you do use one of these for part of the time make sure you adjust your chair to the correct height. I would use the disc for a limited amount of time and build up. I sit on the smooth side, although my mom likes the other side. I'm going to try it while I'm sewing today and see if it helps.