I don't know much about Revolution, but my vet swears by the Program. And so far I've never had any problem with it. It's a shot that lasts for 6 months, and - in the words of the vet - it's flea birth control. Cat gets shot. Flea bites cat. Flea is sterilized. If fleas are already a problem, I wouldn't recommend it, because it doesn't really kill them. It just fixes it so that the population dies out due to not being able to lay eggs.