In my case, necessity.
The original pickups in my 1980 Series bass were cracked, one was microphonic and weak. I bought a new pair of AXY FatBoys and installed them as a temporary fix until I could send the bass out for repairs, upgrades, and ultimately, a new set of Series single-coils.
If I recall correctly, the magnets in FatBoys are the same size as in Series pickups, but there two coils in the shell, hence the humcancelling capability within.
You have a very good ear, and would be able to tell the difference. I can tell them from the SC-1's in my '77. It's probably 95-97% of the way. Me personally, I think the real wizardry is in the Series electronics. The pickups get you that last little smidge... and the Series single-coils simply are more sensitive than their self humcancelling counterparts. They just are. I could live and work without that 3-5%, but can totally respect that some can't.
I seem to remember reading somewhere here, part of the drawback to the humcancelling AXY pickups is that the coils are stacked, putting the magnets much closer to the ones in the coil that's 'listening'to the strings, unlike the Series pickups, where the humcanceller coil is at a standoff distance. Having those coils elsewhere is an advantage; the ones picking up the strings aren't being influenced by anything else.
They still sounded amazing to me, and I continue to believe it's mostly to do with all those squiggly little wires and doodads inside that I don't understand.
