Me too, hopefully they federate at some point. The team behind Hardcover seem to support the ideas of the open web.... at least data portability and so on. Let's see if a meaningful connection with Bookwyrm is possible in the future.
I'm no user myself (yet?) but according to their "sidebar" (whatever you call that info on Mastodon) it's hosted by a German NGO.
This means they have to follow German laws which may be stricter than other countries in some areas. As an official NGO they likely also have pretty active moderation. Other than that they have pretty common rules (no harassment, doxxing etc).