both of them have flip-up sight (MAD), they are visually identical. Are they coming from the same source? What are the differences between them?

Avoid the ASA sight: I picked up one from Brownells while placing a big order, and found that it did not hold zero when you flipped the sight down, then up, and that it actually damaged my upper receiver because it rubbed against the rail.

The only difference I can see in its design is that the MAD has only 2 aperture sizes, while the ASA has 4. The reasoning behind the MAD is that you can turn the dial either way and get the other aperture size. To ASA's credit, they arranged the apertures 1-3-2-4 in order of size, such that you would always get a much different aperture with a 90 degree turn of the disc.

I haven't tried the MAD, but knowing GG&G, it should not have the problems of the ASA sight...

I decided that I would go with one of the Knight's units, although I haven't gotten it yet.

Julian

Neither, go with the ARMS #4o as you don't have to push it up, especialy if you want a sight that goes back into battery automaticaly. That's why it's the biggest seller to combat users that are able to choose.
Good Shootin, Jack

What he said!

ARMS #40 is the way to go.

I had the same trouble.