Recommendation: Which Guitar Support Could Be Better For Me?

Because of back problem, I am planning to buy one of the guitars supports below:

a. ErgoPlay Tappert Classical Guitar Support (http://tinyurl.com/luhjbwo)

b. A-Frame Guitar Support (Link: http://tinyurl.com/nqfr9sq)

c. Dynarette Guitar Cushion (http://tinyurl.com/os75rr4)

Has anybody purchased one of those guitar supports? Any recommendation?