There are several key differences in favour of Crosspass. Note that a recipient must already have the Signal app installed before a sender can share anything with him by Signal. Also, the sender needs to know the recipient’s phone number. However, most business communication is done via email, and asking a recipient for a phone number would be an intrusion into his privacy.
This usability difficulty is a consequence of the asymmetric cryptography on which Instant Messengers are based. With asymmetric cryptography, a message can only be encrypted if a public key of the recipient has been registered with the API server beforehand. In contrast, Crosspass does not have this restriction. A Crosspass share is assigned a lookup ID and a PIN independently of a recipient and the sender can immediately include them in his communication.