I would always discuss this with your own vet: there is a wide range of products available now, but availablity varies with location (some products in some countries, not in others). Frontline is fipronil, and there are multiple generic branded versions of this now. It works well, for the right cases, with no evidence of resistance or inefficiency. Herb powders are not generally nearly as effective.
Vets are increasingly asking “does this individual cat need to be on regular flea preventives?” – because not all cats do. It depends on the risk. And this is another reason why this is worth discussing with your vet in person, as they will have a good understanding of your own situation.

There is a solid system for reporting and storing all complaints about possible drug reactions: that is how the system works. Even if they do not get back to you individually, the database of possible reactions is there for all to see, and if any trends emerge, appropriate action will be taken.
The truth is that all products licensed for cats have been proven by evidence to be safe and effective in nearly all cases: if this were not so, they would not be granted a licence.
This does not meant that individual reactions never occur: they do, but they are very rare. And they happen with flea shampoos, by the way.
It is not all about “love of money”. It’s about helping cats with safe, effective medications, with the acceptance that very rarely, there may be side effects.