Not open source, you can't verify the end-to-end encryption or any other measures the client uses actually happen. This makes it trivial to hide backdoors.

The entire secure messaging app space is open source, why anyone would bother with writing a proprietary app and thus omit verifiability of the security claims is beyond me.

EDIT: Also, no proxy settings, meaning your IP address can't be masked with Tor/SOCKS5 proxy.

Do NOT use.

It doesn't appear to be open source, so users have no control or lasting guarantees of privacy.