This is an amazing product. I have arthritis of the spine and spend many hours per week orchestral playing. Not all the chairs we are expected to sit on in different venues are suitable for the purpose. However, with the use of this back support, I am able to play in comfort for long periods. The cost on Amazon is minimal, but the advantages are enormous, making it possible to maintain a good sitting position, thus taking stress off the spine.
One word of warning which is not a criticism of the back support in the least, but rather of chair design,is that it doesn't function too well on chairs that have incomplete backs. In other words, if there is a strip of wood/ plastic at the top of the chair back and then a great void where the lower part of your back should be able to rest comfortably, the back support system just falls through the void because it has nothing to rest against. Dreadful chairs!!
Ordering through Amazon meant that it arrived very quickly, and was, all in all, a very worthwhile and cost effective purchase. Try one, you'll love it!!