How many of those are any good and not snake-oil crap?

The FDA publishes withdrawal notices in the Federal Register [1]. The withdrawal rate for reasons of effectiveness is something like ~1/yr.

[1]: https://www.federalregister.gov/agencies/food-and-drug-admin...

Withdrawal notices are only related to active harm and not efficacy AFAIK

We could have many compounds out there that don't do anything for their intended target but aren't actively harmful