I really wouldn't go that far - I actually HAVE a Marshall half-stack, and you just don't get the same feeling as you do when there's actually a 4x12 involved. The tone just isn't the same either. You just can't emulate an actual 4x12 cabinet. You can EQ a thick tone, but it isn't going to make a combo, or even a 2x12 sound like a 4x12.
It's not going to be exact, but it actually does make it sound bigger - not just bassier. Really well thought out low end on that pedal.