@Scilly.Suffolk There are two models of Gorilla... the plain old gorilla and the gorilla XT, I have both and both are good.
I use the XT versions behind the saddle and they are the most secure options I've tried for that position... noticeably stronger than the plain gorillas that they replaced. I did loose a bottle last ride, but that was the first one since I installed them 6 months ago.
I use the plain gorilla on my BTA mount and although it isn't as strong as the XT i find it fine in that position. I've only lost a single bottle from there (annoyingly in a race when it was my only nutrition so I had to go back for it).
I currently have an Xlab mount behind the saddle (not sure which) but for me, that speedfil R3 looks ideal for my needs. Next season...