Go with the low profile gas block and then you can mount optics or fold down front and rear sights. Gas block will not stick up above your free float handguard. DPMS has several options on the gas blocks.
The gun in the photo is using a Yankee Hill system (Low Profile Gas block and specter hand guard that free floats over the gas block). I used the same system on my second build, and my third build used a similar system. You can ran a gas block that has a flip up front sight, or a rail (to add a sight), or even a unit that has no provision for a sight option. Just be sure that the gas tube length matches the system the barrel was setup for (carbine, mid, or rifle length).
How do you explain a dog named Sauer without first telling the story of a Puppy named Sig?
R.I.P. Sig, 08/21/2019 - 11/18/2019
Low profile gas block under a free float tube or rail.
"I am a Free Man, regardless of what set of 'rules' surround me. When I find them tolerable, I tolerate them. When I find them obnoxious, I ignore them. I remain free, because I know and understand that I alone bear full responsibility for everything I do, or chose not to do."