My Camelbak-knockoff (made by schwinn, I think, for cyclists) flat out saved me during my FTX. First off, it had double the capacity of my canteen. So between the two of them, I could carry 3L of water. (Keeping in mind that I'm still stuck with the '82 webbing.) The hsoe allowed me two get at my water at any time I had two or three spare seconds. About the only time I wasn't drinking was during section attacks, or on the defence when I was under fire. I kept the canteen as a refill for my camelbak when we were taking a break for a couple minutes.
On ruck marches, it can be a bit of a pain the butt, but generally I'll just stick the camelback into the top of it, and feed the hose into the D-rings on my ruck straps. As long as I have a couple spare minutes when I drop my ruck, I can haul it out and wear it over my webbing.
By far, this was THE BEST piece of kit I've EVER purchased. The only con is that refilling it can be a minor hassle, particularly from Jerry cans, but it's well worth it.
On my SQ course, we have an OC from the PPCLI- he lets us use whichever kit we want in the field, as long as it doens't make us less effective. Apparently that's rare for courses, but it's a pretty lcuky break from us. My MCpl and Sgt also wear them regularly, and both are from my unit, so I anticipate being able to use it on regular unit exercises.
I hope to get an issued one at some point, but I know that that's unlikely any time soon, as they're still ops-only issue as far as I know. For the time being, any civvie pattern of duitable colour is a good buy.