I used a signal mirror a lot some years ago (in SAR operations - guiding the chopper in, indicating your location to other teams, etc., and they are extremely effective, efficient signaling tools. i don't obsess about which particular type or the "aiming technology - five minutes practice with whatever mirror you have will make you an expert. Back when I used one routinely, I did carry a heavier glass military type signal mirror. Now that it is less likely to be used, I depend upon the mirror in my compass - it is real glass and the compass case protects it just fine. Some of my kits contain the plastic shaving mirrors with the reflective surface protected by a plastic sleeve

No one ever seems to mention it, but a mirror is really great for lighting up the entrances to mine shafts and caverns.