Thanks for the input everyone.
Why only considering the Apeks? well, for a certain level of future proof really. It's the same (ish) price as the Gekko and better featured BUT I'd rather have something that does what I want now (and probably for the future) and will be reliable rather than get something that I MAY use in the future on the off chance I get more adventurous. If the Apeks was as reliable as the Gekko then I would get it but through all the research I've done the best comments I can find are "I think the Apeks are better now", which doesn't really cut it for me when I'm going to be 20m under the sea.
Besides, I now know the Gekko does NDT's and they seem to command a decent 2nd hand price so I'd never be losing out that much if I did want to upgrade. I think my mind's made up
Oh, and I'll be sure to search for Shagra
edit: are their any recommended accessories to buy (face covers, lanyards etc)?