A shatterproof acrylic mirror, 2.75 in. x 4.25 in. (7 x 11 cm), 0.7 oz. (20 g). Integrated lanyard hole.

Twenty grams. That is the entire argument. It is less than an ounce, it will not break, and at that weight there is no decision to make about whether to bring it.

Acrylic rather than glass or steel: lighter than both and, unlike glass, it will not become a hazard in your pack.

The integrated lanyard hole hangs it from a tent loop or a branch.

Acrylic scratches more easily than glass, so keep it in a sleeve or a pocket rather than loose with your stove. If it is going to live rough in a camp box, buy the stainless steel one instead.

This is a grooming mirror, not a signal mirror. Coghlan's does not give it an aiming hole or a sighting grid, and without one you cannot reliably aim a reflection at an aircraft. If you want a mirror for rescue signalling, buy a purpose-built signal mirror — do not rely on this one.