The small aperture is for long range, the big one is for close up. Only thing I dont like about the MBUS is that the apertures are too hard to switch between. They arent like a normal sight. If you have no fingernails, they can be hard to switch. But for a backup, I love them. I wouldnt use them as primary sights though.

And of course I like Magpul. They make great shit. lol