Good write up, exactly what I was looking for. I just ordered the Comp spoiler for my coupe and got Betalink just in case. I really like the thought of using 3M tape like you did, because I heard betalink is royal pain, so I think I am just going to follow in your footsteps. BTW thank you for the link to the photos.
15 M4 / 14 M235i-Sold / 09 E92 M3-Sold / 07 E92 335i-Sold