How it works on 7D: Press half-shutter and keep it pressed -> ring-buffering pics until button is released. Then cam will calculate focus for each pic and stores them in order of focus precision. Number 0 will go to best focus, highest number to least focussed. Works as designed, I suppose.
What 650D does: Most images viewed during in-cam processing and in Photoshop are garbled, only about 1-3 pics are not messed up. Lowest numbered pic (always good) doesn't seem to be the best focussed.
Don't know if other D5 cams are working or not.
Minor issue: Wording. Says "Best focus" in submenu, "Best Shots" in Shoot menu.