I'm not sure what I think, to be honest, as I've never been able to find reports of independent clinical trials (if anyone knows of any, please let me know) but if you do want to give it a try, CC is right to recommend VetUK. Moreover, if you click through to VetUK from a rescue, that rescue gets 5% commission from VetUK at no extra cost to you.
Paws Inn is in the scheme
http://www.pawsinncats.com/ as is Chesterfield CP, to my certain knowledge.