Copyclaiming my own videos?

So my YT channel was recently demonetized and I've gotten a few contacts asking me to put some copyrighted music on my videos and they would auto-copyright claim it. So this raises a few questions that I'm looking answers to:

1. Does this actually work?
2. If yes is this legal/allowed?
3. If both above are true shouldn't I just get copyrights to a song on my own and then copyclaim my own videos? It doesn't look too difficult and the people who have contacted me have proposed pretty bad shares (they'd take 30-50%).

I'd go with #3 if you own the copyrights to the sound recording you'd be using and can legitimately make the claim in Content ID. The easiest thing would be to find one of many distributors out there that deliver metadata and recordings to YouTube on your behalf (DistroKid, CD Baby, etc.). Just make sure you do have the rights to the recording, that would turn bad real fast if you didn't.

I don't like becoming reliant on an organization to pay you rather than just getting your cut via Google which is consistently paid out.

Is this company reputable from what you've researched or do they just have an email address?