I’ve tried several in ARs, plastic pistols, and 1911s.
In the polymer pistols and ARs the triggers hinge and a flat trigger is supposed to give you a mechanical advantage and make the trigger feel lighter than it is. It the opposite is also true—If you pull at the top it feels heavier. And with a flat trigger I’d never quite hit the exact same spot with my finger so the trigger pull was always inconsistent from string to string. So I gave up on them but some people don’t seem to have that problem.
