The RG-UF/M is an interesting platform to start experimenting with. If you are not built like the Governator, you can dive it unfer reasonable workloads.
Very compact, ideal for long shallow dives, or to be used as a donor rig. The CMF valve though is not for deep use.
I have played with these things quite extensively and they are easy to modify and rebuild without any special tools.
GKAM's Rebreather Pages GKAM's Rebreather Pages 
I have a couple for sale if you are interested.
/George