My gripe with BKPs is that certain pickups sound REALLY good in certain guitars and the same pickups might sound like shit in another. With BKPs, it's all about finding a good pair that work well in your guitar.
I had a Blackmachine B2 with Nailbombs in it that I thought was flubby, muddy and just overall very lackluster. The guitar itself played like a dream though and I wouldn't fault the sound of the guitar with the pickups to the builder at all, it's just the combination of tone woods with that particular pickup that were not to my liking. However, I have the same pickups in my Jackson SL2H and they absolutely SLAY in that guitar. Tightest, clearest pickups I've ever heard in my life with that guitar. I also had Painkillers in an Ibanez Prestige and I thought they were just "okay," they sounded good, but nothing to write home about over a good set of Duncans, however, I swapped the pickups in that guitar with the Duncans in my Les Paul and the LP came to life. Keep in mind, both of these guitars were using the same type of woods throughout each of them, the Ibanez actually weighed more than the LP, the only difference (besides the Lo-Pro Edge on the Ibanez) was the neck in the Ibanez was maple and the neck in the LP was mahogany, the difference in sound between the two guitars was GIANT though with the same exact pickup. The BKP just mixed much better with the Les Paul than it did with the Ibanez.