I run a Kill flash for two reasons
1. a cheap protective barrier that will save my lens from scratch,s dings, etc ( I don't run a front cover on it)
2. The kill-flash darkens the sight picture just slightly... that small amount of Contrast makes the dot easier to see in bright sunlight making acquisition of the dot to the target easier and quicker.
If your not working for Uncle Sugar and your running one for any other reason your wasting your money........
The two reasons I stated are not it's intended purpose, but a by product of it's primary purpose which is to Eliminate (Kill) the unwanted flash that light reflecting off the front lens can cause... which may give away you position in a tactical environment .You know Kill-flash.....
Don't buy them new... look around... they can be had for cheap..... if protection and sight picture is not a big deal fr you.... then buy $25 in ammo.. or 2 new magazines.........