Mag primers will generate more burn on initial strike. Unless I am wrong somehow, this always leads to slightlly higher chamber pressure (for a given powder). Whether that is "good" (or not) is entirely objective. Unless you actually measure it, you may be playing with fire (so to speak). Of course, one cannot say for sure that isn't a good thing either (as - again - you can only know if the pressure is actually measured).
Of noted interested is use of Magnum primers in large projectile cartridges when combined with slower powders. I can't comment intelligently on this use, but there is some precendent to it...