Have used them quite a few times over the years with (in general) a fair bit of success. Really need to test individual tubes to see how good they are. Obviously the o-ring needs to be in good condition (grease it up) & the main flaw is that the attachment point is also likely to be the main cause of failure. What I mean is that you need to really crank the lid closed but then if you're clipping it on to a harness then you're likely to be using the ring/handle and it's easy to loosen the lid this way. Might be an idea to put some snoopy loops around the tube & then put a crab into this?
Other issue with rocket tubes is that they actually have a pretty small capacity (ribs inside them) but they're a bugger to get rid of. Oh, and pretty buoyant so might need to attach a bit of lead to the outside. And my memory is pretty shite but I know that I've used them down to at least 25m. Well, I say "I know" but what I actually mean is "I think"!!!