In information technologies there are three main security goals: Confidentiality, Integrity, Availability. And while Signal is really good with the first two it utterly fails with the last one (at least on iOS).
Still I use Signal every day and would also recommend it to everybody who just wants a good private instant messaging client. While I also like and use Matrix (and see a bright future for the protocoll) there are still far too many problems to use it stress-free and smothly in everyday life.