I own the Kingston Turbochip 400 which is bascially the same thing as the 366 (just different AMD K6-2 CPU's). Its not that rare

Depending on the revision you own it might not fit into every Socket 5 board. This is due to height of the CPU socket conflicting with the soldering on the backside of the adapter. I've only seen such sloppy soldering on the Turbochip (the Powerleap and Evergreen Spectra are fine) and it may be fixed with a soldering iron.

Even though it supports Socket 5, it is in reality only 430FX boards. Other boards may work, but only with Pentium CPUs in the adapter. You can look at my Socket 5 ASUS P54TP4 motherboard thread for a bit more information on such adapters. ASUS PCI/I-P54TP4 Socket 5 motherboard thread/review