What this guy did was add M5 bodywork to his base ass 525i. He had everything. Front bumper, rear bumper, side skirts, and fenders with the vent. All unpainted and still rocking the 525 badge on the back.
I’m assuming none of this was cheap to do. I am baffled on why you wouldn’t just spend the extra money to get a 535 with a tune and other performance bits. That way you have a legitimately quick car that isn’t a poser-mobile for the same price as building this.