The Cygnus Distortion/Sustainer is adapted from the Pete Cornish G-2, a Big Muff-based circuit.
Cornish pedals are probably best known for being extremely expensive. There are two reasons for this. First, the build quality and reliability is unmatched. Second, the mysterious nature of them, partially due to the fact that the circuit is obscured and partially because of the A-list of clients. (The G-2 is most famously used by David Gilmour.)
Inside, the circuit is a basic Big Muff with a few changes such as the use of germanium diodes for clipping instead of silicon, and of course the famous class-A transistor buffer design. Both buffers together (the bypass buffer and effect input buffer) have almost as many parts as the main circuit!
The Cygnus is a faithful reproduction of the G-2 circuit, but with one major update: an internal switch allowing the pedal to be used in true-bypass mode instead of buffered bypass. As with the Klon KTR, the buffer mode is “almost always better”, but you can be the judge of that.