I see Eric Anholt is now recommending compton with OpenGL as the compositor of choice for Raspberry Pi - https://github.com/chjj/compton/issues/390
So I've enabled the armhf build of my packages for compiz-reloaded ( https://launchpad.net/~adamsmith/+archive/ubuntu/compiz-reloaded ) for you to try. On low end hardware that I have I've found it to be better than compton.
Just a follow up.....I have this running on a raspberry pi B 512MB! (compiled on raspbian)
I've opened an issue report on the vc4 mesa github to track any problems...