I prefer flip down rear and pinned front with ACOG.
As rugged and tough as the ACOG is, there's very little chance you'll ever need the BUIS, but it's still nice to know they're there.
I didn't fight to defend your freedom so you could vote to take away mine.
"A man who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself.
John Stuart Mill."