I used one for almost 200 dives.
I did (after about 75 dives) remove the Mares guts, and hoses, and regs, and just used the jacket as a regular BCD, which it was fine as.
The cons listed above are apt... except... while the systems are integrated, they are able to be seperated (as I did); however... the first stage is rigged to work with extra large hoses (to fit their manifolds) so the first stage would need many adaptors to make it work with standard hoses. The BCD part works fine on its own without the extra stuff in there.
If you can find a good deal on one, it makes a decent beginners system....