When it comes to flea treatment, I recommend going with the one your vet recommends. Cedarcide is a rebrand of wondercide after a class action lawsuit surrounding their claims about ingredients. Both cedarcide and vets best are unregulated essential oil based products and that has the inherent risk of any essential oil around cats. Their livers don't do great with processing oils and exposing them to essentials oils could have a long term health impact. I get the desire to avoid chemicals but using the vet recommended product for your region ensures that any flea problem is taken care of without worrying about unknowns.
Agree with the Kieka. First you discuss this question with your vet.
Second - check the description of particular med on Pet express website and make sure you know all the side effects etc etc
Third - give it to your cat and watch him/her closely in case something goes wrong.