I'm sure its been said in this thread before, and it will be said again. Rebreather diving is not for everyone!
If you're a regular trimix deep diver though, you'll save yourself a bucket load on the cost of helium (just saying).
The most important thing to me, as a CCR instructor at both recreational and technical level is that the training you are given is taken seriously. Due to the potential for hypoxia, hyperoxia and hypercapnia (on top of all the normal OC risks one might encounter) a CCR diver needs to be more alert to what they're doing and what they're breathing. If we instill during training a small dollop of fear and a large dollop of respect, people take the training seriously, monitor their gas, understand and practice their bail-out routines and live happily ever after as a CCR diver. I find, personally, its really not that hard to monitor your PO2 constantly on a dive, and I prefer to dive a mechanical CCR too. If it weren't for the cost of scrubber in the tropics, I'd dive CCR practically every dive.
But like I said, Rebreather diving is not for everyone.
My buddy, and tech CCR instructor, Jon and I pulled together this (long) video on CCR diving for beginners, where we even go into some detail to show you 'how' a rebreather works (in a very simplistic way). Of course I think its excellent, but check it out too