I have built the T-16 OTL amp and the Grounded Grid preamp. Not difficult if you work carefully. I'm not an EE and my only wiring/soldering experience has come from building kits since adolescence. The owner is very accessible and is very willing to help out if problems arise. The amp is not a kit for a newby, though.
Sound was to die for. Only problem is the T-16's relatively low output and my having relatively inefficient speakers (in addition to my Quads). When paired with my Quad 63's, I got really nice music. Perhaps one day I'll look at his "The Beast." You'll likely miss the OTL sound, once you've heard it.
Of course, YMMV and I have no affiliation with the manufacturer other than being a satisfied customer. Good luck,