The market is moving on from that - longer slim tube free floats with no rail that extend past the lo profile gas block are now the trend. The flip up BUIS is a superior sight vs a rail mounted one as it's on the barrel and protected from the pressures on the handguard.
As said, tho, pinning one on requires some gunsmith level machine work, as the gas block has to be held rigidly in place, and accurately, while drilling, and it won't match up with any pre-existing holes. If anything, pictures bring out that those holes aren't all that accurately placed either.
Had the barrel been grooved and long gun screws used, the same affect would have been accomplished, a tightly fastened gas block resistant to a lot of beating. However, the AR was designed to eliminate as much machining as possible -so it got drilled, pins inserted, and they were peened over. Non replaceable, and no way to lose them in unauthorized disassembly. For a civilian sporting rifle, it just complicates any further changes the owner may want to make.
I used a clamp on FSB, and now that I'm shopping to replace the issue handguards for a free float tube, it's going to be easy to make that change. I won't have drilled pinholes to ruin the looks of the barrel, I can do the work myself, and the likelihood of it causing me to miss a shot, which would be extremely rare, would mean a whitetail deer lived a few hours longer in hunting season. Recreational guns aren't life and death - and if it is, then you get one issued to you. Pinning gas blocks on isn't the end all be all of AR building.
Given the limited choices available and the likelihood that future changes can occur, I'd buy the clamp on setup that appeals to you the most, knowing it won't make a major difference until you choose to do something different, at which point it will make a difference, in your favor.
