Love this little mirror. Took a survival course a few years ago and saw the difference between plastic and glass mirrors. You want glass if you're ever stuck out for any period of time. The sight hole is nice, but learn to use the "v" finger method to sight the mirror. A mirror is handy in general anyway; I use mine to check for ticks, view my face when I've gotten scratched by mesquite thorns, etc, etc. Also, for a case I wrap with duct tape. This is great for a survival kit as you can easily put a couple yards of duct on the slip, the duct tape protects the mirror well, and the length of the mirror make a convenient length of tape to tear off. I love this little mirror.
I've carried this mirror every time I go into the outdoors, since the early 90's in the military. Excellent for everything stated in the other reviews: finding ticks, first aid, hygene, redirecting light, or it's intended purpose - a signal mirror. Mine still has most of the original signaling instructions printed on the back.
I personally prefer the clarity of glass for my camp/signal mirror, but you should keep in mind this mirror will not float if you're planning to spend some time over open water. I carry the glass mirror in my drysack, and keep an acrylic floating mirror in the pocket of my flotation vest when kayaking.
Being made of glass has its advantages - it is durable, doesn't rust and won't break or scratch. This mirror is always in my backpack for the impromptu weekend trip/day hike. I even bring it with me scuba diving (signaling for help in case I'm left behind after the dive). For the review above: No pouch? Get a used bicycle inner tube from your bike store, cut a 3 inch section and pull it over the mirror and you have some protection for it.
I am very impressed with the reflective quality of this mirror. The only "problem" with the mirror is that it does not have a scratch-resistant, break-resistant carry pouch and can slide out of the foam pouch provided. Being glass, it can shatter and cause injury. Other than that, I really like the mirror and I have purchased several to give as gifts to my hiking buddies!
Older version of this mirror is not waterproof, however that changed in 2010. "The new watertight design can be distinguished from the older design by the details of the lanyard hole. The new waterproof design has a beveled/countersunk lanyard hole that lacks the metal grommet present in the older non-watertight design".
Note that the mirror pictured by REI is the older model.