Given how aggressive Apple is in protecting their walled garden, I don't expect this to survive the litigation. Apple tends to ignore individual hackers (look at hackintoshes) but businesses making money off unauthorized use of their APIs don't last very long before the tidal wave of lawyers come.
Maybe, but seeing the recent scrutiny they have had for not allowing sideloading of apps, killing this might actually push legislation against it. As an android user, I wouldn't use this app even if I had access to it because it's not secure and because I don't give a shit about blue bubbles.
The company behind the feature Nothing is advertising, Sunbird, claims that their solution preserves iMessage's end-to-end encryption. They also claim they have figured out how to handle thousands of accounts on a single Mac. Both problems Beeper hasn't been able to solve.
Unfortunately they have failed to provide any details about how they accomplish these things, which has Ars Technica feeling pretty skeptical about the whole endeavor.
You are logging with your apple ID into a Mac mini in a server farm somewhere in the world, and it acts as a relay to send you your imessages over their closed source app, that does not mean secure to me at all, even MKBHD was a little iffy about the security of this service.
Maybe in the EU, but I would have little hope for the US market. The US has been astonishingly slow to take adverse action against companies within their own borders for the past 25 years. Believe me, I hope Apple and Google get what is coming to them, but I won't hold my breath.