I tried the product (Johnsons Home Flea Dog/Cat Spray, 250ml per can) hoping it would get rid of the fleas we had. Sadly, nothing much came of it! I suppose the smell might have been enough to scare them off for a couple of days but certainly, by the end of the week, we were suffering again. We've since tried other products to help clear the pests out. It'll take time, I think.
With a 250ml can of spray, you need to check how many cans you'll require depending on how many rooms you have. You're meant to spray at a distance of 38cms for 8 seconds per square metre of flooring. That takes some doing! Be aware that this stuff is marked as extremely flammable. Keep it stored away safely if there's any left after you've sprayed your home.