I have it and used it in the past. It’s better in privacy than Signal since it’s decentralized and doesn’t use any identifiers. Signal forces you to use the worst identifier ever: your phone number. It should be optional (as Threema) for easy contact discovery, not mandatory. Back to SimpleX, I stopped using it because every time you have to connect the computer to phone if you want to use it from computer (it’s for maximum security, but inconvenient for me). But it’s a great app.