My wife and I use these attached to our seat rails. We are commuters and enjoy exploring our city on the weekends by bike. They really do work. Vehicles give us a much wider berth when passing. The triangle, when flapping in the wind, is visible from hundreds of feet away. I wouldn't ride without one now.
I love these things, I have one on the back of my rack on the touring bike and on my backpack when I'm riding bikes without a rack. On narrow mountain roads and commuting in the evenings, cars see the slow moving vehicle symbol and they give me plenty of space as they pass. There are 2 strips of Velcro that makes for fairly easy fastening. I also like the added security of having this in conjunction with the battery powered blinky. I've seen a larger version of this that you wear around your waist but that just looks too goofy and cumbersome, this one strikes a good balance between form and function.
Has velcro straps so it can be slipped onto your back pack or hung on the back of your bike, jacket, etc.
Should work well for riding at night and in the rain. Flashing lights also help a lot.
I keep the Aardvark attached to my rear seat for all rides to add a margin of safety in a hostile road environment. This is especially true riding at twilight or evening when visibility is a must to prevent by hit by a vehicle approaching from the rear.
This is so nice to be able to have just another aid for drivers to be able to see you. I put this on my rear bag of my bike and feel a lot better about being visible during rush hour traffic. I am excited to put it to use on my Pacific Coast trail bike ride in July.