So go for it! We may own the book, but we don’t own the right to comment on it. There are tons of other sites out there that comment on book covers — it’s to be expected that there’s overlap. We sometimes use a book cover after another site. Sometimes other sites use book covers after us. (And sometimes they use the scans from our site to do it, but that’s a whole other issue.)
Just, you know, do your own thing with it. Which I know you would. :-P I like seeing what other people have to say about them. We’re just two people, trying to come up with something funny on our own. There’s a whole world of people who have different ideas about them!