I used Signal from the TextSecure days up until shortly after they removed SMS support. Removing SMS support nuked most of my contact list, as it turns out 'default text messaging app with opportunistic encryption' is a much easier sell than 'just another messaging app installed alongside others and then largely ignored'. I suppose this may have played out differently if I had more iOS users, privacy dorks and activists in my orbit. After months of no messages coming in and annoyed responses via other apps by people wondering why I wasn't just using those, I deleted my longstanding account.
Last year I registered again at the request of a new friend, and have been disappointed to find that Signal still has occasional sending and notification issues, though not as bad as in the past. I have one former contact who refuses to try it again, as they originally registered at the height of these issues several years ago and wrote it off as a trash app run by incompetents. First impressions matter a lot I suppose.
For all its downsides (Google, metadata privacy, etc.), RCS had been much more reliable than Signal ever was up until the breaking changes a month ago, and obviously far more ubiquitous. I hope we eventually have a FOSS implementation of RCS, as it would make Signal redundant for most use cases that don't require an extreme privacy focus.