It is the styling that is different but I highly doubt the CM bespoke suits (especially the well regarded ones) cannot or does not have the same quality when it comes to constructing a suit. Bespoke has more to offer than OTR. You're paying for GBS because of style preference.
Thing is under low or artificial lighting, which these events are mostly held, the midnight blue looks richer than black. Pairing it with black trousers may end up looking like you have a mismatched black jacket and black trousers.