I need a flip up sight as a back-up sight on my lastest AR.  I have an ARMS #40 on another AR but I wanted something differnt on this one.  The upper I am mounting this on is a RRA M4 style post-ban upper.  
I would like some information and/or feedback on the GGG MAD flip up sight.  I have never seen or used one of the GGG sights so any input on this sight would be appreciated.  
To anyone that has used one:
What did you like or dislike about the sight?  How ges it compare to the ARMS #40?
Where is the best to get one?
What is the going price on these sights?
Thanks in advance,
KW

MAD is a good sight, the different aparture is really cool to play with.  I personally like the #40 better, because of the spring loaded action.