The output of both is more or less the same. The HFS has accentuated treble and midrange. So, its a pickup that needs some care with the amp settings. You can't just plug it into any random amp an have it sound good. Its finicky. If you don't take the time to dial it in, its going to be very shrill and ice picky. However, once you hit that sweet spot, it's massive for thick searing leads. The M is more scooped in the EQ. It thumps in the low end and sings in the high end, but is more rounded off in the top end which avoids that shrillness of the HFS. So, its a pickup that doesn't have to be dialed in just to sound good. On neutral amp setttings on my JVM (everything set to noon), its quite good. The greatest difference between the HFS and M can be found when playing clean. The M cleans are as good as any alnico mag pickup I've ever heard. Usually you don't bother playing cleans with ceramic pickups but the M is beautiful in that regard. The cleans on the HFS are pretty lousy, no matter what you do with the amp.