I am planning on using this sight on my flattop.

Here's a few questions:

-I can choose between the standard version and the A2 version. Part of the reason I am building an AR is that I want to nail my Army rifle qual every year. Thus, I should get the A2 version, right?
-I hope to add some sort of optic at some point. I understand that the idea behind a "BUIS" is that you can use your iron sight if your optic goes down. On an M4 setup, how does the BUIS function when you have an EOTECH or ACOG in front of it? Perhaps this question reveals significant ignorance, but i just don't get how this works...

Thanks for your info.