What good will inspecting the factory do? Sounds like a design issue with the pills. They should be questioning some chemist in an office, not observing low caste peasants pouring pill juice into machinery and declaring it all good.
And verifying that a factory has adequate QC doesn't just mean walking the factory floor to check everything is correct (although that is a good start). It also means checking that the factory has a QC program: that management has implemented quality checks and acts on quality issues; that staff are able to flag issues (without retaliation and with reports that get acted on); that they demand the same from suppliers etc etc.
We absolutely need the FDA going to factories, not (just) to observe the actual technicians but to inspect the overall way the factory functions wrt quality.
In the case of potassium pills, they should be quality-testing the extended release mechanism. It's possible an inspector wouldn't be able to catch that their quality testing is shoddy or non-existent in every specific case, but if they show up and see a pattern of bad manufacturing processes, that's important to act on.