Well I've never played the Black Star, but I have tried the other 2 and can comment on them.
The BOM - great high gain sounds. Bit too much for me, but I did think it could be very useful if you like that sort of thing. It has an almost fuzz-like character but more tight and focused than I generally consider a fuzz to be. Has a versatile EQ. It, IMO, isn't really for modern metal though - more metal is the 'traditional' sense, if there is such a thing.
The Body Rot - I don't usually like to slag off a pedal but man did this one suck, IMO. I did not like it at all. Horrible, shrill and for me, totally unusable. Just nasty and not in a good way. Also, the one I tried kept crapping out. To be fair, I never tried it with my rig - I played it for a while in a shop through a Fender Twin, which may not be the best amp for the job. Nevertheless, I didn't hear enough to make me want to take it home and try it on one of my amps.
I have the Black Star and have played the Body Rot 2. The BS is smoother and at my favorite setting sounds very Marshall stack. I keep the tone all the way down. I think it brings in some artificial fizz when turned up. This pedal seems to morph into a fuzz when the gain knobs are cranked up. The BR2 sounds the most like a big fat Recto than any other pedal I've tried. I also have the 6 knob Tube Zone and while a lot of people say it sounds like a Recto, I think it doesn't quite have the grit and raspyness that a Recto has. The BR2 has it. Huge low end chunk, too. Very brutal sounding. I'd like to get one some day.