Dumbles are hand-wired hand-built guitar amplifiers. They have a bit of a myth built up around them because Alexander (Howard) Dumble, the builder, makes so few of them. Custom order only and very expensive. Used by Carlos Santana, Robben Ford, Larry Carlton, David Lindley, the late Lowell George and Stevie Ray Vaughan, Steve Kimock, Henry Kaiser and others - very clean sounding and extremely touch sensitive. The Overdrive Special is known in some circles to be the Holy Grail of Fender-style amps. There is also, reportedly, significant variation in quality of tone from one Dumble to another - so I would think one would want to play a Dumble before buying. So goes the short version of the story. IIRC Valentino mentioned them here and has perhaps played through one.
Two-Rock is making amps that are very close to the kind of tone for which Dumbles are known.
Overpriced? Perhaps. But look at what an early Strat is fetching these days. If this one goes for 15K I would estimate that to be a bargain.
Tom