In the words of Reuss Musical Instruments:

Supreme sounding 1960s germanium ‘face’ fuzz built with rare NPN germanium transistors for modern, pedalboard friendly power polarity
The sound is 100% vintage authentic, and the NPN properties of the transistors makes it possible to power the circuit with modern, negative ground polarity, without the need for additional charge pump circuitry. This is a big advantage over vintage original PNP germanium pedals, which can be tricky to integrate in a modern pedalboard because of their reverse power polarity (positive ground). No need for an isolated power supply for the Purple Faze!