like i've said many times before, the bass knob isnt the filling, fattening bass many of us are familiar. rather, its a "make cab bigger" knob. and given i get a mostly room shaking feel from that knob, i think its more of a shelving kind of circuit that many either like or dislike. for my needs, tho, especially w/ my 1x12 cabs, i love it! makes a little 1x12 seems much more enveloping than it seems.
Actually, it seems to NOT be a shelving control, which is the most common type of bass control on most heads that I'm familiar with (if it is a shelving control, it behaves quite unusually for one). I agree it does work differently than most bass controls. It will add a TON of low end that seems to be centered on the mid bass and high bass areas, versus the more general 'extension' of the deep low end with more standard shelving controls like the Aguilar, Markbass, Glock, Eden, TecAmp, GK, etc., etc. type 'bass' controls.
I agree, if you need big low end fatness, especially in a cab that needs help down there, it's great. If you need to roll deep low end out of your sound in a difficult room...not so much.