Please be cautious about using
online pet pharmacies.
Also, the problem with using flea collars is not the brand, but the chemical being used. Because there is no way to control dosage in a collar, animals are frequently overdosed. If you have to use one, cut the "tag" off.
Here's a couple of articles about
Frontline and
Revolution. They break down the chemicals used and how they are transported through the animal's system. If you are going to use an "off brand" of these medications, please double check the main ingredient. Frequently, the "off brand" is a concentrated form of dog flea/tick dip (some version of a pyrethrin). Pyrethrins can be toxic to cats.