As said above, pinned is as solid as it gets. There are jigs available for low profile gas blocks.
Clamp on blocks are supposed to put less stress ( affect accuracy less) than dimples and set screws. They also hold well when correctly installed.
I have not seen a gas block come loose that was set screwed and have one LaRue barrel with their 3 screw gas block. As long as it's covered by the rail, tightened farmer tight with loctite, it should be okay.
