Yes, you still have engine breaking. Yes, if you stall on the side of a hill climb, the bike will roll backward. However, you will not stall the motor, and you can keep the bike from rolling backward by rolling on the throttle slightly.
I started with a Revloc two years ago. I sold the bike with the Revloc, and riding the new bike without a centrifugal clutch reminded me of how much I like the clutch. I put the Rekluse on the new bike two days ago, and like it even more than the Revloc. It is smoother.
It takes a while to learn to use it to it's maximum advantage, but once you do, you won't want do without it.
TomM