This was one of those pedals I picked up on a whim, it was at the right price and I'd been curious.
The BD-2 is a decent sort of overdrive fuzz. It's really dependent on the gain settings.
Mine is currently unmodded.
While I like a lot of Boss's pedals, what strikes me time and again is that they filter the low frequencies too severely. This one suffers the same problem as the SD-1. Nice dirt but no rumble.
I'm sure it's a simple mod, but since I have the SD-1 the way I like it, I can't really be bothered.
I'm told it's better on humbuckers, but I only have single coil pickups on my guitars.
With a few tweaks, I'm sure this pedal would come up smelling roses.