Just remember, vets, like doctors, have "pharmaceutical" representatives visit them and are often convinced to go with the "new and improved" for various reasons, including incentives. If something is working and has a good price point, don't necessarily change.
When I took Peaches to the vet for her annual visit here in CA, the vet didn't even carry most of the common meds anymore. I refused to purchase others, knowing I've had a terrible time with her and fleas and what I'm doing now is working. Not messing with a good thing. I should have thought and gotten a prescription from them and ordered on line ... duh!