The downtime I understand being a concern, especially for laypeople. The GP comment specifically identified Signal's secretiveness surrounding their server as the dealbreaker that made them "fine with WhatsApp", which is what I was actually responding to (didn't make that clear).

That said, Re: downtime, I've been using Signal for years now with non-techie family, and I've never had any complaints from them outside of that one two-day window. Signal is doing remarkably well even today. It seems like they just failed to adapt to the massive spike in load they had that week.