I would definitely suggest getting the litter box screen from BB. I have one, and it is one of my best purchases! I haven't seen any sore hocks on my rabbits feet, so I guess its not that rough on their paws. But if your rabbit is very heavy (LIke 7 pounds or something) you might want to put a bit of hay over the screen, as their feet can tend to get sore easier.
Also, if your rabbit is a dwarf, or has small poops (hehe) then they may just fall through the screen, so...LOL