I want to use SimpleX for communication not necessarily tied to my real identity while I use Signal for communicate with those have my phone number. Does it function flawlessly like Signal?
No lag during calls? I’m curious if it’s smooth like Signal.
It’s certainly a bit rougher around the edges than Signal, especially with group chats. It’s also certainly less buggy than Session.
I think you should just give it a try and see if it will work for you anyways, but no, I haven’t seen any private/secure messengers that Just Work 
in the same way Signal does (yet).
I’ve been using it sparingly for a while. It’s been working without issue for me. Group chat improved recently, it’s still under development.
The only issue I see is that some other people using it in my group chat won’t receive message until they reopen the app. I’m pretty sure it’s linked to aggressive battery saving of smartphone, and the fix is on dontkillmyapp.com. since simplex is not as popular as Facebook, it won’t get added to exclusion list for the aggressive battery optimization.