Plenty of amps have variable NFB controls, including most Peters amps, Mezzabarba, and some others I'm not remembering off the top of my head. It's just a pot wired as a variable resistor in place of the typical fixed-value NFB resistor. Pretty easy to implement into any amp. But when a company like Bogner gives it a whacky name, suddenly it's "new" and "innovative" I guess. And no, having a variable NFB control does not negate the standard depth and presence controls. It's akin to changing the slope resistor in the tone stack. Having a variable slope resistor (which some amps have), does not negate the individual bass/mid/treble controls. Global NFB control shifts the entire amp's NFB and the the individual depth/presence still function within that shifted range.