I have seen a Krieghoff 375 H&H double with muzzlebreaks on both bbls that looked like Answer Systems.
I have a bolt rifle in 300 Win Mag and 375 H&H with Magna-Port, and I like them. They do not seem any louder to me [the shooter] but they would be louder to the PH.

I seem to remember a double rifle that was Magna Ported, it had the top trapezoidal cuts, just not the side ovals.
I think it would affect regulation.