Here is my take as someone who absolutely loves the work simplex did on the SMP protocol, but still does not use SimpleX Chat.
First the trivial stuff:
no one else seems to use it
UX is not great because of initial exchange
These two are not that unexpected. Any other chat app with E2E security has tricky UX, and SimpleX takes the hard road by not trading off security/privacy for UX. I think this is a plus, but yes it annoys people.
Now for the reasons that really keep me away:
the desktop app is way behind the mobile app - and I would really prefer to use a desktop CLI app
haskell puts me off a bit - the language is fine I just don’t know how to read it - for more practical issues it did not support older (arm6/7) devices which kept lots of people in older devices away
AFAIK no alternative implementations of either the client or the SMP server exist - which is a petty I think the protocol would shine in other contexts (like push notifications)
I was going to say that there are not many 3rd party user groups - but I just found out about the directory service (shame on me, maybe? can’t seem to find groups though)
protocol features/stabilization is a moving target and most of the fancy new features don’t really interest me (i don’t care much about audio/video)
stabilization of code/dependencies would help package the server/client in more linux distros, which I think would help adoption among the tech folk
Finally a couple of points on some of the other comments:
multi device support - no protocol out there can do multi device properly (not signal, none really) so i’m ok with biting the bullet on this
VC funding is a drag - but I am still thankful that they clearly specified the chat protocol separate from the message relay, which means that even if the chat app dies, SMP could still be used for other stuff.