I like flap holsters a lot, especially for carry or hunting guns while navigating thick brush.
Best if that flap is REALLY stout and closes really positively so the gun won't fall out even if you "go inverted" It's real nice to still have your big blue friend with you at the end of the aerobatics!
How do I know this? Here's a hint: "whiteout"dense tule fog and a deer trail about one fawn azz wide down in the Snake River Breaks. (And it's not the last time I performed an inverted loop without benefit of aircraft....).