I suspect the difference in character from one Mean 90 to the next is... due to the fact that when you're buying a $30-$40 import pickup, you don't get the QC you'd expect from Duncan and others. They probably vary widely in sound.QUOTE]
That's my concern with any Asian-made PU's, the lack of consistency, along with lower quality materials. While I haven't tried GFS PU's, I've had so many muddy Asian PU's that I'm gun-shy about all of them. I agree, some are better than others, but none have ever had the clarity & definition of a high-quality American PU. But then, GFS is competing on price, not tone. Their market is the guys who want a better sound in their import guitar than the stock Asian PU's, but don't want to spend the money for good ones. Like their target is a middle ground of guys willing to settle for less tonally. You may get lucky and get one that sounds as good as a Gibson or Duncan, but don't count on it.
I still think the best option is to get a used American-made P-90, so that you have some assurance of what you're getting. Not much price difference at that point. And if you happen to get a GFS that's not particularly well-made or good-sounding, what then? Buy another? Get a Duncan? Trying to get out of it cheap with a GFS may mean you end up spending more. Some guys like them, others don't. I'd rather not take the gamble myself.