Just gave it a quick bash!
VERY thick and heavy, just like the TFR with a bit more upper mids. It can deal with me pegging the low B on my loud passive Yamaha BB, which overloads the front end of most other muffs I've tried except the TFR and BBM.
Massive lows, they thump nicely too, I wouldn't need to use a blend with this. Even playing with a pick that normally sounds thin and trebly, you get a massive sub bass punch using this.
One difference I noticed to the BBM, if I dig in hard on that pedal with both PJ pickups on, it produces a nice overdrive like growl. On the Russian it just sounds the same but louder and heavier, like this is your tone now and you ain't changing it! Not necessarily a bad thing either.
It gets my seal of approval anyway, I'll stick it on the board for a bit and see how it fares in a full band mix!