Hartung OTL Mono Block Amps

These amps are frequently offered for sale new on ebay from the designer/builder and sometimes show up on audiogon as well. Even after considering the discount for purchasing direct as opposed to purchasing from a dealer, the price seems low compared to the more well known OTL amps when comparing features and specs.

Does anyone have experience or first hand knowledge of these OTL mono block amplifiers, e.g., sonics, reliability, fit and finish? A fault in the old Futterman OTL amps would propagate to the speakers and cause extensive damage. Most of the current well known manufacturers say that their design precludes speaker damage as a result of an OTL amp fault.