Along with not changing flash hiders, you can add not being able to change gas block/FSB and barrel nuts. Therefore, you lose one of the great advantages of the AR platform, the ability to change parts and customise. You are pretty much stuck with the gasblock and handguard setup you started with. Since a 16" barrel with a basic flash hider or comp is only about 17.2", that's a big price to pay for that inch or so.

