I have 2 barrels for my Blaser R 93 that are Magna- Ported.
A 300 Win Mag, and a 375 H&H. I have shot both of them side by side with Blaser bbls that were not Magna-Ported.
I can tell a lot of difference between the bbls. Magna Port takes the sharp "RAP", and the muzzle jump out of the recoil.
They do not seem any louder in the field to me.

I like them.

I have used KDF muzzle breaks. They reduce the recoil of a 300 Weatherby Mag to less than a 308. More like a 243. They are LOUD, however they do work.
Phil Kohen [sp?] Is a great guy and does great work.