I love GK.
Like everyone else here, apparantly, I run everything flat and tweak it depending on my mood or what bass I'm using.
I got my 400RB-IV for £350 from GAK 5 years ago and never had a problem with it. The boost function is great and can really add some nice textures if you use a reverb or chorus with it. I find the amp very versatile too, the EQ knobs being very responsive and even the 400 can get very very loud! I dare to think how loud a 1001 gets! I don't think I've ever had it past 12 o'clock and I've used it to keep up with a loud drummer and two loud guitarists and a very loud vocalist in a very loud metal band.
Of course, peoples opinions differ, but they are quality amps. I don't think anyone could disagree with that.
Honestly, if it got stolen tonight, I'd buy a new one tomorrow... or maybe next month when I get paid.
Truckstop