The Mag-na -ports will not blow back debris and harm the scope on a 7.5" FA. I consider the ports to be worthwhile on a scoped gun. My .475's and one .454 are ported. My .500 WE and one .454 are not. All are useable, it's a matter of personal preference, and the type of loads to be used.
However, about a dozen years ago, 2 friends and I did thorough tests on 3 different 7.5" .454 Mdl. 83's. Porting reduced max. velocity an average of 125 fps in that caliber on those guns. Loss in a .475 should be less (less pressure and velocity to begin with). Not a big deal in my opinion, but one should be aware of the probability before deciding.