And what about TLS? Since Let’s Encrypt certs are free and easily available.
Also no MAC, hard/impossible key rotation and possible performance issues on many Android devices if your data gets just little bigger.
And if you thinking about fixing these issues just don’t, leave it to professionals who know what they are doing and use proven crypto protocols. And again DON’T FUCK AROUND WITH CRYPTO, IT’S REALLY FUCKING HARD TO DO IT RIGHT.