I installed mine this weekend along with the mirror caps, and while I spent a lot of time being precise, the installation was super easy. I still have another day before I can take off the tape, but so far the fit looks good. While I did do some measuring, it was to confirm that it was in the right position AFTER I did a "feel" fit based on how the ends of the spoiler were sitting. I'll post photos later this week once the tape is off. Here are some tips from me.
Pre-installation tips:
1) Check the 3M tape on your spoiler. Make sure that no piece of the tape is overlapping another layer of tape or comes too close to the edge.
2) If there is an overlap, either adjust the tape or cut out one layer of the overlap. Adjust or trim off any tape that it too close to the edge.
3) If you have any rattling, it's probably carbon fibre pieces from when they drilled holes in the spoiler. You can remove them through the same holes by using a vacuum.
4) Prep the area. This means if you have any wax or coatings on the car, remove those and then clean the area with a quick wash and alcohol cleaning (I used 91% isopropyl and a microfiber cloth).
Installation tips:
1) Use the painters tape alignment method from their newer video. This one uses the rear tail lights as the alignment point for your tape. When you lay the spoiler on top, you may have a bit of overlap on each side. I did with mine.
2) Peel the center pieces of tape off the spoiler and make sure the spoiler is sitting on the trunk rear edge
2) You should slide it back and forth slowly to see how the two ends are sitting. As you move one direction or the other, you'll see the ends get closer and closer to the rear but at some point you'll see the gap widening, that's when you know you've gone too far and need to go in the other direction. Using this methodology and checking both sides as you do, you can kind of hone in on the sweet spot where you'll have minimal gap (if any) on both sides.
3) You can double check centering after the methodology above using the tape guidelines you laid out before. You can also confirm with measuring the center of the spoiler and aligning with the T (be sure to confirm that your T is actually centered).
4) Peel the front tape pigtail and gently press one side as you move across.
5) Do the same for the rear tape pigtail.
6) Press firmly, I suggest starting from the center and moving outwards towards the ends.
7) Tape down the ends. My left side was slightly higher than the other.
~Paik