I have mirrors in the cage and for the most part my piggers ignore them. Occasionally they'll take a quick look in passing, but they've mostly gotten over the novelty. Instead of a bird mirror, I bought a visor mirror at a parts store. The clips that normally slide over the visor slide nicely over the cube wires.
Mine have a large mirror in their cage. Every time they walk past they admire themselves in it. Lottie gets freaked out at mirrors while she out during floor time but doesn't mind them in her cage.
Someone on here has piggy who has nose-offs and rumbles at his reflection though.
Lina likes her bird mirror. It the only toy she will play with regularly. I think she likes the bell on it more then the mirror though since she holds the plastic chain in her mouth and rattles it like mad.
Tomoyo likes to look in the mirror. Sakura's too busy sleeping and pushing Tomoyo around to bother, Kero thinks it's ok and I haven't put it in Spinel's cage yet, but I will when Lina gets tired of it.