I used to use Ubuntu Touch on my OnePlus One for quite a while and it was very nice! I had to switch away because it didn't really support group MMS (still doesn't from what I can tell), and then later US carriers started requiring VoLTE which it didn't support for a while either. But I still hope to switch back someday, that was the most enjoyable phone I'd used since the N900.
I haven't tried to use it full time for the same reason that I haven't tried to take the plunge to the dumb-phone world.
A part of me occasionally considers buying one of those cheap KaiOS dumbphones, because I figure that the stuff that's missing could be supplemented with my laptop. The problem I'm always afraid of is that I'm afraid that I'll be missing something. I'll start a job and they'll require some specific proprietary 2FA app, for example. Also, I don't think Signal has a dumb phone app yet and that's basically all I use to communicate.
Similarly, I haven't done anything but play with Ubuntu Touch, because I know there would be an app missing that I would need, so I'd be forced to have an Android or iPhone for those edge cases anyway.
Startup costs are enormous to break into the smartphone world now, at least if you want to penetrate into the "non-tech-enthusiast" market.