Just an obvious pattern of coccidia from a breeder during a certain time frame speaks a lot. Even if most reviews are positive, coccidia is not a headache that most people want or have the time to go through. I hope you don’t have to deal with it. I’m not trying to rude at all, but at this point I think I’d suggest petco/pet smart over flchams. Not criticizing you for your purchase either, normally I think the same way about bad reviews(people usually only post the negative). In this case it’s more like Russian roulette.
So with that said, definitely keep an eye on him and get fecal exams(sometimes one won’t show and you have to wait a few weeks after). If you’re good with/have a microscope you can do it yourself and save some money over long run. Look for the little circles like the name implies, probably plenty of slides on google.
Chances are you’ll be fine, not saying it’s guaranteed. Just a heads up.