Sometimes I think genuine compliments from strangers are the nicest kind, because they can often offer a different perspective than a person's close friends. So even if a person has read only a few posts by any given person, or doesn't really know them that well, they can make observations based on what they do know.

Anyway, I think this is a really sweet idea, and I think everyone will be able to understand if a person makes a general comment. After all, "I don't know you that well" isn't a criticism at all, and I don't see why it should make a person feel bad.