These lights have so many uses, other than just dangling on a key ring waiting to be used to find a slot to put your key into.
The red or blue ones can be used to surreptitiously read a map in tactical darkness; be strung on the back of a pack so that others can follow you in pitch darkness, and can help you find the socks that the cat dragged under the bed.
I've got a bunch of these lights in various colors. Gee, blue ones can even help follow blood trails in the dark, should you be into that nocturnal activity.