All of the plugins I looked at have a "view source" button that takes me to a github repo (though the payments plugin link is broken). Presumably you could install the plugin from source as well... would that not be a better signal than number of users?

At this point you could probably just run it through an LLM yourself and ask it if it does what it claims, if the code is straightforward, or if there are any seemingly obfuscated bits. If something is on a safety-critical path, you should probably do the review yourself.