Here's DiMarzio's word on their Bluesbucker:
Bluesbucker® DP163 / DP163F
And now for something completely different: the Bluesbucker® looks like a standard humbucker but sounds like a P-90. This means any guitar with standard-size humbuckers can now have the sound of P-90s, without altering the instrument and without noise. Patented Virtual Vintage and Airbucker technology let the Bluesbucker® "see" a narrow string window like a true single-coil, making it extremely open and sensitive to playing dynamics. When a pair of these pickups are on together, they achieve the open, slightly hollow sound two single-coils produce. Splitting the coils produces a sound similar to that of a Strat pickup, with very little drop in output. The Bluesbucker® is available in all color combinations as well as with nickel or gold-plated covers.
Tech Talk:
The coil with the 6 adjustable slotted poles is the "hot" coil. The coil with the solid poles is along for the ride to cancel hum and look cool. Since one coil is doing most of the work, the direction the Bluesbucker® is installed makes an obvious difference in the sound. When the hot coil is closest to the bridge, the sound is brighter; towards the neck is warmer. Even though the look is a little nontraditional, we like the sound of the
bridge pickup "backwards" (with the screw coil towards the neck). With a Bluesbucker® in the neck position with the screw coil towards the bridge (also "backwards") the combined sound is Tele-like. With the
neck pickup in the more traditional direction, the combination is like two P-90s.
If this direct quote from the DiMarzio site is against the rules, I'll delete the content and post the link.