It’s already in the same screen, both on Android and iOS, so of course it is much better, and not less convenient, to shutdown instead.
I can’t think of any reason not to, besides “I might want to unlock it real quick”, which is exactly what you’re preventing on this scenario.
Let’s Encrypt is a trusted, established alternative, it could replace Microsoft for long-lived software certificates.
Or tarnish its name associating it with malware and bad actors, who knows?