I'd love to hear more particulars about your test - range, sun to target angle, airplane altitude, airspeed. I have yet to locate a cooperative pilot for signal mirror testing. I do have some WWII RAF test reports on 2"x2" steel mirrors (low reflectivity), and the RAF (unlike the US Navy, USAF, and USCG) felt that, since the 2"x2" steel mirrors seemed to be bright enough to travel the range at which a survivor could see a small airplane, that they were big and bright enough. ( I'm actually supposed to be putting those reports online so you folks can see them, rather than chatting here).

Myself, I'm more comfortable with larger mirrors, and every US Government document and photo I've seen referring to US Government issue signal mirrors refers to mirrors that are 2"x3" or larger.

However, in the realm of 2"x2" or smaller plastic signal mirrors, the Mini Rescue Flash seems the brightest. The beam from my 1.5"x2" Mini Rescue Flash™ (American Medical Kits) is much tighter and brighter than my 2"x2" Mayday Signal Mirror (BCB International), based on today's test*. See the comparison of the beam brightness at right.




All other things being equal, the Mini will be more visible than the Mayday, visible at longer range, and it is smaller, as well.

The Mayday mirror has some advantages over the Mini: it is widely available, comes with a lanyard, floats, is inexpensive, and has instructions on the back.

I've seen one review arguing that the BCB mirror isn't very robust: (video of user tearing mirror apart here:
http://youtube.com/watch?v=8xfao47WHtQ )

The Mini Rescue Flash isn't perfect. As noted, it doesn't seem available by itself, it doesn't float, and doesn't come with a lanyard. After 1 year in my trunk (in Southern California) mine shows some signs of delamination - likely because of the heat cycles. Unlike most signal mirrors, the Mini lacks self-contained instructions on the back. The back (shown here)
http://www.equipped.org/pp/briefs/pic_amk_sol.htm#d
says to go to www.adventuremedicalkits.com for instructions, rarely an option when you get lost. Even if you (as you should) try to learn to use the mirror prior to getting lost, finding the instructions at the website is a real challenge.

The closest I've found is this AMK product video: "Ed Viesturs Survival Essentials", which covers signal mirror use starting about 30 seconds in, and is more easily found on YouTube:
http://www.youtube.com/watch?v=FV_kVLnydlU

I like Doug Ritter's instructions better:
http://www.equipped.org/psp/psp_rescueflash.htm



I didn't try this myself, but I do notice that the sighting window on most mirrors is larger than that in the Mayday mirror.
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* Test Description
I took both mirrors, which have been together in my trunk since last summer, and propped them on my driveway, as shown, so as to reflect the sun onto the back of my darkened garage, 33 feet away. I then photographed the beam.