I love them too, especially the Armson. I sighted mine in at 25 yards (75ft) and get 3 to 4 inch groups.
1- Both eyes are open and that means no loss of peripheral vision
2- They're damn near indestructable
3- Bright, well-defined 5 mil dot
4- Low profile on my markers
5- Does not require batteries.... batteries bad... beer good.... (not sure how that's related but it needed to be said)