My switch on that guitar (Blacktop Jaguar) broke, so while I'm waiting for its replacement, only the bridge position is currently working. I decided to gamble on a cheap switch from eBay for once, and it's been on a slow boat from china for like a month. Hopefully it gets here soon.
The bridge pickup is great though. It's kind of what I've always hoped WRHBs would sound like but they never did. It's thicker than my Fender single coils, has more mids but not in a hyped or overwound way, but still has that immediacy to the string attack that you only get with alnico polepieces, and much more clarity to the treble than a PAF.
Compared to a TV Classic Plus, my favourite side-by-side bridge humbuckers, it's got more midrange, more bass, and more output, along with a smoother string attack, but it isn't any less clear-sounding. It's less clangy and percussive, less sharp, and more throaty, kind of like when you compare a Telecaster bridge pickup to a Strat.
I don't have any other Firebirds to compare it to at the moment, though. Fab winds his FBs with 43 AWG rather than the vintage 42, but targets a similar output wind. This renders the resistance useless when comparing to 42 AWG pickups, as his read a couple of kohm higher without necessarily being overwound or higher output. The conventional wisdom is that thinner wire gives more midrange, but that isn't necesssrily true - it's just often used by winders in order to overwind pickups by fitting more turns onto the space of a given bobbin.
So, I'm not sure how it would compare head to head with a vintage wound 42 AWG Lollar, for example, but I really hate overwound/mid-heavy humbuckers, and I really like this one. Overall, it succeeded at what I hoped it would - being a very clear-sounding humbucker that sounds different from any of my other current pickups. Hopefully I'll be able to report on the neck pickup and the Big Birds soon.