I have one (not for sale I am afraid) and it is fantastic. It allows us to use the same saddle on different horses and to accomodate changes in shape etc. It is great, but you need to be shown how to use it properly. Ours is from Sue Carson and she showed us how to alter it and fit it properly. I would really recommend you get proper advice on how to alter etc as opposed to just buying one second hand.
I have one and used it for ages, my horse changes shape very quickly for various reasons so it was invaluable. I would echo being shown how to set it up properly, it's easy to have too much air in and it has to be balanced. I eventually bought a WOW saddle which incorporates the Flair system. I would sell the korrector if you are interested.