I use the StarFlash mirror, which is plastic.

Read the mirror section in Equipped.org for more info.

I've also used the BSA metal mirror, but it isn't nearly as reflective as the StarFlash. For me, glass mirrors are just too heavy and breakable.

One problem I have with the StarFlash is the aiming mechanism - I find it hard to use while wearing glasses. The two-handed aiming mechanism works fine for me though (hold mirror near eye, hold other hand out in line with target, then flash the hand in front of the target with mirror, sweep back & forth across hand/target).