And? It lowers the attack surface of Immich. Attack surface is about the surface, whatever an attacker can use to get leverage. This acts as an intermediate between Immich and a public viewer, controlling how a threat actor can access a private Immich server. It helps reduce external attack surface while increasing overall system complexity. Since the project is small, it is easy to audit the code.
I like to judge software based on its actually merit and not on the theoretical possibility it is vulnerable. It very well could be vulnerable, but without auditing it we are just speculating, which in the real world means nothing. Every project starts somewhere, without community, followers, and “5 years of support”. I am not saying I would trust this software in a security critical situation, just that your speculation means nothing.