Two years ago, one of my students did his senior project with a NuTube (which was practically brand new at the time, and he was able to get free parts from Korg somehow). The project was a guitar preamp, and he had nothing but problems with it; noise levels were awful, and it took a lot of shielding and HF compensation to keep the thing from squealing/hissing. Now, the student did not lay out a proper PCB (against my protests, but he ultimately ran out of time) and tried using prototype-boards (solder-type) but man, he had a ton of noise problems with that thing. Perhaps Korg has some (actual) reference designs now that address the noise issues. I got the impression that it was a sort of gimmick device.