I tried doing that with a previously unsearched/unsubscribed community as a test on my own instance, and I got a 404: couldnt_find_community error when clicking the link. As you stated, it seems like in most cases that special link will not work unless someone has previously manually searched for the same community in your instance.
I think I’d rather link directly to the instance for the community than get a 404 error. For most people, getting the 404 will just deter them from proceeding further.
Perhaps it would be best to include both links in a post?