Hi Tyler, I'm sorry that you had such a negative experience. I'll try to address some things, but without knowing which Blender version you used, what operating system you are on, which version of the addon was used in your "first session" it will be very difficult for me to fix your exact issues.
1 - As far as I know, it is not possible for this addon to corrupt a project blend file, if you have any more info, or a blend file to test, please send it to me.
2 - Issues with cleanup and class registration were fixed by the Extension review team before the addon was integrated with Blender, though they did exist in prior versions.
3 - The only way I'm aware of to encounter the error you're describing is to have an old copy of the addon from Github, and install a copy from Extensions alongside it.
I can give you more platform-specific tips if you can tell me what operating system you use, there is some manual file management that you can do to get around "poor cleanup".
Please, please, PLEASE follow up with me here, on Github, Mastodon, BlenderArtists, Youtube, anywhere if you have experienced any kind of data loss and you believe the addon is responsible!
I've never had a good experience with this add-on excluding the first session I used it. If the errors start, you start risking your project becoming corrupt and it can't easily be uninstalled due to poor cleanup due to its class registration / unregistration. I do not recommend it in its current state.