First off, they are super stable in rapid firing. That, clearly, is good. They can be set up to be gentle on paint, this too is good.
The efficiency is generally pretty disappointing, however, on a stock Matrix. I am guessing that you are talking about a 2003 model Matrix, rather than a DM4, DM5, or Proto Matrix. There is hope, though. Evolve made a wonderful bolt kit that really improves efficiency. I am told that the newest bolt kit they offer is inferior to the older one, but I haven't tried the newer one to compare them. Apparently something about the original Evolve bolt kit offended Dye so that the newer bolt kit was released to be legally acceptable. This may be the sort of stupid rationalization that someone presented as fact and gets vetted around the internet without factual basis, though, so take it with the salt cellar I serve it with. Peegee comes around here occasionally, so maybe he will see this and comment.
The rubber detentes never really did it for me. I got a lot of stupid breech breaks, and as the rubber detentes wore down, I got more and more, eyes be damned. Then I got the breech from New Designz (why is the "z" mandatory in paintball prodeucts?) with the ball/ spring detentes. I just don't break paint in the old 'trix anymore.
They are bigger and heavier than most modern guns, but for stability and reliability, I can't say I'd rather have a different back-up (actually, at the moment, primary).
Enjoy, shoot faces!