I'm interested in the Hellbender especially, and I love the idea of a Bass boost knob!!!
But do they work well with active bass, 5 banger's etc etc....
It might work acceptably with an active bass if you use the mode switch, but something like a MK II tonebender is really best with a passive bass and a cranked up compressed tube amp. No matter what you do to it it was designed in the 60's for guitar, and having the appropriate gear for something like that really makes or breaks the tone and how much low end presence you'll be able to get out of it.