The 135i guys are going wild for these due to their low cost and no cats. I searched and found no information about using 135 midpipes specifically.
Also forgive my inability to understand how a turbo exhaust makes things different.
n55 on left with no cats:
So using 135i mid pipe would require a 135i axel back
128i 1 piece, notice the cats.
Therefore, the N55 catless mids would make things interesting. Would this throw any CEL or codes??