Aristotle13, get the GG&G flip front BUIS for the gas block with rail.
Except for one upper I have, all my flat tops eventually get a flip front BUIS. Necessary? No, but it just annoys me to see a shadow in my optics due to a sight tower. However, as pointed out, it takes skill or money for someone to install a front flip. I got the PRI, but I actually like the GG&G better cause I just like the looks and it has a bayonet lug to tweek the PC people. Would I use a bayonet on it? Of course not, though I might use an attachment that utilizes the bayonet lug (light/bipod/laser).
My Armalite came with a gas block with rail, and I got the detachable tower, but I like being able to instantly flip the sight up or down and not have to worry about loosing it cause it's been removed from my rifle. I used the GG&G flip for gas block rail and am very happy with it.
With a SHTF rifle, I prefer the standard sight tower. YYMV.