The basic verdict: Cute, fun, recommended if you're a Dumbledore fan or you just feel like doing something nice for JKR and / or Romanian orphans, though probably not worth $12.99 in purely objective terms. Also surprisingly postmodern-feeling. It would be a fine way to introduce one's children to concepts like
metafiction or unreliable narration, although come to think of it, I'm not sure that normal people actually
want to do such a thing. At any rate, it would not surprise me if JKR were a Borges fan.
( Slightly more spoilery notes )