This is the BOA Band, Made by North American Rescue Products, I keep one of these on the top outside of my medbag for quick use. Its simple and works, Just press the little lever at the top which releases the band put it around the needed arm or area and clip it back (as illustrated below) I personally then roll it down alittle to set it in place, start your line and hit the little clip again to release and your done. They come in a sealed package and are pretty durable Ive had the one On my small bag now about a year or so and it still works great!

Its as easy as that and is definately fast and easy, they retail for about 10 bucks each however but it definately worth the money.