Lately my seats had become a torment increasingly on a normal office chair; I kept trying in vain to find a position that caused me no pain in the back or legs. When toward the front slides I stuck my blood flow into the thighs. Looking for alternatives I came to several "loose" chairs, the Gymnasikball and the Swopper.
About the loose chairs I could not find information and the best specimens are me also a bit too expensive (300 euros). An exercise ball is too big and too dangerous (they burst sometime!). A Swopper came for me given the high price (500-600 euros) out of the question, but I could try it once already and was very impressed.
The Sitness 20 is relatively small and unobtrusive, so that he (at least in the early days) easy to store somewhere if you do not want to use it all day. Doing so may mean for inexperienced people too much strain on the back, but is intended to give the time.
I myself am relatively well trained and feel now after 3 hours no complaints. If something clamped or pressed, you just wiggles a little back and forth or backwards and forwards, which makes a lot of fun!
The tires below is actually a "real" tire, which you can inflate variable (air pump included). Unfortunately, he also smells accordingly, but due to the small surface only when rangeht tight and secure itself are still.
The workmanship is overall be described as very good. The two terminals with which the plastic sleeve is attached to the seat are slightly fiddly to install, but otherwise took the building barely 3 minutes and no tool required. Well, for the second terminal I then but a pliers taken ...
The lateral wobbling works perfectly and is exerted consciously or unconsciously constantly; you can sit wonderfully even in semi angekipptem tires because it can not slip. There are a plethora of different sitting postures between which you can change constantly.
The Swopper need a huge floor space and is very hard, this is better. However, unfortunately, the vertical wobbling works not at all; the built-in spring allows for no significant play, so that "up and Abhüpfen" as opposed to Swopper is not possible.
My conclusion: for only 100 euros a good and safe alternative to the office chair and a lot of fun. The seats will be for gymnastic exercise and the back will definitely thank you!
Despite the small drawbacks - due to the reasonable price full 5 stars from me!