If I were you, I would not use it. There is a lot of info on the net that it's not good. Now, I don't know if the info is correct, but I imagine the health of your animals is worth spending a little extra money. http://www.elversonpuzzle.com/biospot.html
Bio Spot uses the same active ingredient as the Hartz Mountain products which have gotten all the bad press for being dangerous to animals, so I'd be very, very cautious. Do your research and only use it if you're convinced it's safe. I'm not.
I have used it in the past as the main chemical is the same as hartz but is half the dosage at least in the dog one.. I cant afford 45 every three weeks for the vet stuff ( I do think this is best) so I use a product that is all natural it works for the last 44 seasons on Kandie and so far no trouble with Gigi or Zoey and can be reapplied every week if nessary .. main ingrediant is the primary in human shampoos
I'd stay away from any of the OTC brands of cat flea killer - I've heard too many horror stories about them.
If you want to use Advantage or Frontline but can't afford to treat multiple pets, you might find this link helpful: Advantage for multi-cat homes (click here) - it's been a lifesaver for me, with 5 cats & 2 dogs in a climate with year-round fleas.