I installed the preamp for 15 days on my Start pickups which show more than 30 years on the clock. I had the choice to change the pickups (very expensive) and may change the sound or find the right combination to recover their youth.
For the modest sum of € 40, I installed the preamp in my guitar and the effect is rather spectacular. The sound regains its biting treble are raised and the power increased significantly, so I Redemont to add a switch to cut back and its fine home when I want.
I see you later install a knob to assay the effect is actually quite violent.
I can not imagine the effect on humbuckers (it can be mounted on all sorts of electronic passive pickups). Considering the price, there's really nothing to do without it, provided it is a little DIY.