I heard that the open-prong FH would also get snagged up in heavy brush. Sounds reasonable, although I never encountered this. I got snagged up plenty, but the rifle never did. $B-)
It did get snagged up and some did use the prongs for opening C Ration cases.
But I do believe the real reason was to cut down on muzzle flash at night. Plus the bottom of the bird cage is solid with was to help with muzzle rise.
Pretty impressive muzzle flash at night with either one.
Never had an issue with the flash hider and brush. On the other hand, the BFA and camo nets were another matter. I swear any time I would get near camo netting with the BFA attached, the two would seek each other out and entangle themselves like demon lovers.