certainly get peoples opinions on units, trust me the last few weeks i have been bugging a few people to tears with endless questions about this and that. and god bless 'em they havent told me to s0d off yet!
but you are doing the right thing asking, and i would certainly recommend trying units as it really does open your eyes to what they have to offer and how they float with you, no pun intended.
for me personally i was inch close to buying a meg after my infield testing, but then looking at the sentinel, the feature that really swung it for me was the canister duration meter and backup meter. granted that this does not gaurantee that you will never ever ever get a CO2 hit, but for my own personal comfort zone this is what is needed at the moment. as i too am new to this Rebreather malarky and unlike some guys, who i am sure can work out their canister durations by simply tasting the CO2, i can not! in the future this might and probably will change, so then i will take it from there. but for me for my first unit i am looking at a sentinel.
and granted this is a new Rebreather and not even properly field tested, i.e. non factory field tested and given to the masses, but looking at its ancestory, i.e. C2R/VR3/Boris i am putting a big bit of trust in that previous development, and again IMVHO its sounds like a pretty good ancestory to me for a Rebreather dont you think? and certainly well within my comfort zone
but i think as a starter for 10, you could do a lost worse than a sentinel.