my experience is that good deals are only available/viable/mutually beneficial when you have direct personal, close connections (please stop sending LinkedIn messages!) to the team. "retail" investing doesn't succeed in this arena.

my opinion is that you should only invest as a lone/lead angel in what you know from your long history in a super niche space where you know all the important cognoscenti from a career full of personal interactions...anything else is a guaranteed loss. fine if you use it as the OP says to learn about a market. though would be better IMO to just volunteer to work at a startup in a new area and learn by doing...which I have done and found highly educational and ultimately rewarding.