Shame on your friend! I firmly believe that insect growth regulators (IGR) are THE key to controlling fleas in the home. Adult fleas comprise only about 5% of the total population....the rest are eggs and pupae. IGR products prevent larvae from maturing into adults (thus killing the population). PRECOR is just one brand name that I am familiar with. You can mix and spray it yourself, it is not harmful to you or your cats. Borax might be irritating to the cats.

Do some research for yourself. I think you'll be convinced.

I have used borax or disodium octaborate tetrahydrate which is just a solubilized form of boric acid. PRECOR is not permitted to be shipped to NY. So I dissolve either borax or octaborate (MOP UP) into water and then dispense with vacuum cleaner. After water dries, the octaborate is left as residue and prevents reinfection of animals with fleas. But if cat or dog is infected, they must be given shots and an application of advantage. A grooming would also help. By combing their fur you can see the fleas on the comb and get an idea of the extent of infection. If they go on your bed or curl against your pants and you lie in bed with your pants, then you will also spread the fleas to your bed. This is an annoying problem. So I wash bed sheet with borax or tetraborate too. I try to prevent pets from curling around my ankles; if I fail, I have to change my pants and put infected pants in washing machine.