Running an MBC bypasses the BPC, correct.
But in doing so you take away the ability of the ECU to pull back boost in case of knock.. In other words you could be running "safe" boost levels, but the engine could ping its as.s off and still ruin the engine. The ECU wont be able to do a thing.
the engine will pull timing if it detects knock which wont be enough to completely remove from danger, but will let you know something isnt right, that is if you know how to feel your car.. not to go against you but i hated the way my apc operated. the one on my 900 operated like a MBC. the one on my 9-3 (still t5) was stupid. limited boost in 1st and 2nd gears. retarded! if you choose to run a MBC you should have the supporting monitoring equipment (boost gauge and wideband an autometer or aem, they are the most accurate. buy cheap get cheap.) stock boost is 10psi +- 2psi fuel cut is 14.5psi (until you get a tune)