The Red Giant is an overacting 1975 Green russian Big Muff copy with some serious thunder-tweaks which make it sound pretty different from the original.
Of course, it's a giant (the "red" is btw no additional allusion to any political system the Muff was born in). And it sounds kinda huge, dry as a bone, a bit less scooped and with an audible hi-roll off. It gives your sound a fat load of compression and a butt kicking low end. The main differences to the EHX-classic are a special selection of different transistor types with a slightly higher gain, a modified tone stack and a changed clipping arrangement. There are also some more smaller mods to tweak and harmonize the entire circuit.
Demo rig:
Guitar: 1990 Gibson Les Paul Standard 498T B / 490R N
Amp: Peavey Valve King (for ordinary/neutral clean sound)
Speakers: Celestion G12-80s in a vintage 4x12 Orange Cab
Room-Mic: Heil PR 30