Yeah, it increases bass.
The second set of screw poles increases the signal that the pickup gets from further toward the neck on the string. Vibrations are wider and basser there, so it gives more bass.
I chose it for that, and to be able to EQ the pickup to some extent, generally and by indiviual string. I've had great success doing that with the warpig (12 screws by default) and my custom MM.
Not a hint of mud from either, too. I think Tims being either modest or advising cautiously there? Best way, really, but my experience of it great. The miracle man w/ double screws in particular has a huge low end, more than the pig by quite a bit, but just as clear a high end as my standard (albeit covered) MM.