Where are you seeing this product? On Ebay?
There are a lot of counterfeit flea control products out there. Please read this EPA warning:
Counterfeit Pesticide Products for Dogs and Cats | Pesticides | US EPA
The only safe place to buy flea control is from your vet or a reputable online pharmacy like Entirely Pets, Drs. Foster & Smith, etc.
If you want to customize doses and save money on multiple pets, why not use Frontline spray? That's what I have used for years on Lady and my two cats. I just pump the recommended amount by weight onto a cosmetic puff (cotton balls are too absorbent) and rub it all over them. One bottle lasts me years - until the expiration date!
Frontline Spray