I'm a big fan of the classic EMG 81/60 set, but I had an extra guitar with passive pickups lying around and I thought I'd give these a try just for fun, instead of having another guitar with an 81/60 set.
I've installed these on a 24.75" scale length guitar with a Tune-o-Matic bridge.
Compared to other passive/PAF pickups, this EMG Fat 55 set is much brighter and more open sounding, but with the same dynamic range.
It's more versatile and can be shaped into more tones, especially if you're using an amp modeler.
You don't get that muddy low-mid boost of a typical passive humbucker, so the sound is much more open, but can sometime be perceived as a somewhat "hollow" if you don't set your amp accordingly.
You do get the high-mid bump that give you that "quacky" sound like a typical PAF, but it sounds a bit wider in terms of the resonant frequency, less narrow and less "honky".
The high end extends way farther than a passive humbucker, so you get that sparkly "HiFi" string sound that helps with note/string definition and adds articulation.
This of course can be filtered off if you don't want it in your sound.
They're quieter than a passive pickup, but not as dead quiet as a classic active EMG set.
Compared to an EMG 81/60 set, the Fat 55 are much brighter overall.
They have less low mids, more high mids, more low end, and less high end.
They're less compressed and give you more dynamics, even when playing with high gain, but it can also be perceived as a less smooth and consistent sound, a bit more "pokey", depending on your preference.
Overall, I still prefer the classic 81/60, as I'm not a big fan of the passive pickup sound.
However, if you're someone who likes the PAF sound but wished it was more versatile, open, and clear sounding, these are for you.