The question "which mirror" invokes almost as much discussion as "which knife."

My personal thought process and opinion:

• For PSK purposes, plastic is better than glass (given weight, fragility and buoyancy characteristics).

• Plastic isn't as reflective as glass, so I shoot for the best plastic version I can get.

• My self-imposed rule for outdoor "stuff" – if the cost is under $25 for any item, then I'll get the best available, no matter that it might be considered "expensive" compared to competing versions. Especially important for one of the "essentials."

• I believe that Rescue Reflectors are the best-of-breed among plastic signal mirrors Rescue Reflectors. Each is handmade, and they're individually tested. Mr. Murray, the owner/maker, is somewhat of a "signal mirror" guru. If you visit the website, click the "Specifications" box at far-left for some interesting reading.

I've seen any number of independent comparisons on the web; here's one such at Sea Kayaker magazine: http://www.seakayakermag.com/2001/01Oct/mirror4.htm

And Doug includes a discussion here on ETS website.

I have no affiliation with Rescue Reflectors, other than being a happy owner.