It is true. I have a green Russian Big Muff and I use it in most songs. I play Jazzmasters Strats and Teles, copies and vintage clunkers too, even an acoustic electric epiphone through a Marshall JCM800... the OLD 2203... a 100w stadium head and a 300w custom Cab of 3 Fender Speakers and an EV. Love the sound I get. My soundscape ranges from Goth to Grunge, Hard rock to industrial and back again to ballads and musical salads.
Here's what that statement IS NOT saying.
Through my big old valve amp that is built to scream, the big muff sounds great RUNNING WITH OTHER PEDALS. With a tube screamer it is mighty. With TWO tubescreamers... pick a better word and double it. With a compressor it is a beautiful thrummed note that does not know the meaning of "decay" or "Stop Sustaining". With a flanger and some delay it is a sad listful sound, with a phaser it screels through the swooping overtones of the phase....ignoring the notes you are trying to play like they no longer matter... surrendering to the waveform. Slapped alongside a marshall emulating pedal it tries to crumble in a comforting way and with a soul food (Klon Clone by people who didn't really try) It can bring you close to tonebender and rangemaster-esque tones. With a wah it wails or hums, depending on position in the signal chain. and slap an eq pedal before it and you can emulate chugging palm mute Djent work.
By itself it is a good pedal. but it is how it works with others that makes it unique and where it's versitility comes into play.
Through my solid state amp... Roland Jazz Chorus.... it misses the mark, drives everything a bit too aggressively and unpleasantly and has me tapping other pedals instead. Even through fender amps the tone is a bit thin and brash. And don't put it anywhere near a vox.... It is a workhorse and the vox is a show dog... you know what happens when you try and plug a horse into a dog...
not recommended.
And with a bass this thing thuds like a champion.
It even adds some real guts to drum machine tracks and sets up perfectly for industrial voicings otherwise unattainable.
The Green russian is a bassier version, with more bottom end and a more stable midrange presence. Closest comparable for the best price is the EHX Bass Big Muff Nano.... not the normal Big Muff Nano. Or even grab an ENO BMF fuzz from ebay in china.
That will give you a feel for a great sound match for minimal dollars.
There are plenty of boutiques about... all charging heaps for their approximation of a pretty simple circuit. It is still in production which says something for it... don't pay the big bucks when you can work magic with a basic version.
Hope this helps...