We don't put any sort of flea/tick preventative on Fionn MacCool - he's an indoor cat, and doesn't seem to be troubled by fleas. Another thing that helps is that we brush him almost daily, spring though fall. Not only does he love it, but this keeps our house from becoming a hair farm and lets us see if there are fleas.
Perusing the Product Guide I was horrified by just how many products are toxic to cats. Anything with Permethrin (causing muscle tremors, seizures, salivation, vomiting and even death) or Pyrethins (signs of pyrethin poisoning may include coughing, wheezing, shortness of breath, runny or stuffy nose, chest pain or difficulty breathing) should not be used.
Do NOT use essential oils on cats - no Pennyroyal, Tea Tree, Citronella, Eucalyptus, Lavender, Geranium or Rue Oil. It is toxic, and can kill them.
Do NOT use flea collars intended for dogs on cats.
To learn more, please see the Green Paws Toxic Fact Sheet