Yup the 12 is the offset in mm. Check out the sticky in this forum for info about offset vs. backspacing, it's basically 2 ways of saying the same thing. The B on Discount's website denotes black finish. AM is anthracite machined, MM is mirror machined, C is chrome, etc.

The specs for this wheel are the same as the MB Predator wheel. However, no one has verified whether these wheels fit or not. Someone has to test fit to see if they clear the calipers. Whether or not it clears doesn't just depend on the backspacing/offset, it also depends on the wheel design (shape of the rim itself), so there's no way to know whether it clears the calipers until you try.

I have asked this before, at thenewx.org, but no one answered if it had been tried. And don't feel bad for asking - this thread is about whether this particular wheel (Unique 297) fits, which is a good question to ask, there are no other specific threads about this model. I don't have a discount tire where I live, otherwise I would have already dropped by to have them test fit it. Anyone who's near an actual store, PLEASE go test it out! Although I'm not holding my breath - the shape of the rim looks like it tapers too slowly, and it doesn't look like the calipers will fit in there.