I'm a programmer myself and have been part of many security centric projects on my long IT career. Based on the information they have provided on Sayphr website, on live video and marketing video, it's quite clear to me how they are different. All secure messenger apps that I'm aware of use servers in the middle. When you send a message i.e. in Signal to someone, the message is stored in encrypted form on Signal's server. This alone is not an issue. In other messengers however, when you connect with someone, you get a public key in a plain text format of whom you're connecting with from a server. In order for the connection to be secure, communicating parties should always verify out of band that public key signatures match. How many people know that? Not many based on my experience. So basically Signal's server could give you their own public key, which would mean that they get access to your unencrypted messages. Also if you take quantum computers in the game, you are in trouble. Pretty much all cryptographic protocols like Signal protocol are vulnerable to Shor's quantum algorithm. This means that by knowing a public key (Signal's server knows), a quantum computer can figure out the private key in a reasonable time.
In Sayphr:
- encrypted messages are sent directly from device to device (P2P)
- public keys are exchanged out of band (MITM attack not possible)
- messages are encrypted by using quantum safe algorithms (not vulnerable to attack by using Shor's algorithm)
This all is just based on my knowledge. I'm not saying that these are facts, so make sure to google yourself.
