Well it looks like a total ripoff of the Sharp Shooters Supply design magazine, and at the same price. There is something that does worry me about this magazine he list it as having a "Custom made coiled spring" this is where a lot of people get into trouble. If the spring is not made form the correct wire, it will take a set, and cause many problems. The other concern is that it may not work properly to begin with, this may be the wrong type of spring to work in this application.
http://www.darkeaglecustom.com/products.shtml