As a former user I felt these pain points trying to do nothing more than have a very active one-on-one chat with a good friend. Tens of messages an hour, maybe 2 years running. Using matrix.org and the pre-X clients. It's fine for group chat (IRC style) but that's not a high bar.

(a) the encryption between using a mobile and the webapp desyncs/breaks all the time, it just sucks. I mean you'll get "cannot decrypt" a lot, have to bounce back and forth and generally try and force it to re-sync properly again. Sometimes never worked at all. Lots of issues on GH over the years.

(b) as mentioned in this article, insane delays on new message notif and sending and receiving. Just logging in on the webapp every morning took minutes of some sort of mysterious sync process, often the mobile app had the same problems. The X stuff may fix this, we were pre-X.

(c) cleanup. There's no message retention set on matrix.org, when I wanted to extract and remove our past chats the process and experience was excruciatingly bad. It took tens of hours over several weekends of the webapp (mobile completely non-op in practice for this) polling and loading old content, just so I could select 100 at a time to delete and then it took an hour. Once I started culling back over a year or so, the loading got longer and longer and longer, until eventually it 100% stopped working at all to load old messages.

Signal and DeltaChat are far, far better experiences for one-on-one chats with friends & family. The Delta client is a bit UI/UX behind but not horrible; e.g. you can't correct a typo in a sent message in Delta, unlike Signal - because each msg is a unique gpg-encrypted "email" rather than a database object that can be re-manipulated.