After inspecting the diffuser more carefully I noticed a few flaws.
There were some very slight weave imperfections but they are not in easily visible spots.
One of the tabs was not drilled, but the dimple was there for the hole.
The biggest issue I saw is the fact that the weave is pulled a little bit in some areas. It is indiscernible to the naked eye, so it is not a weave imperfection. It does, however, allow light to leak through from behind the weave. My car is MR, so I didn't want to take any chances of having the red bleed through from behind the thin CF.
I taped and spray painted the under side [inside] of the diffuser satin black. It took more than a few coats but it worked; nice solid black that prevents light from bleeding through.
Also, there was no double sided tape included, which was okay with me since I was planning on removing whatever it came with in favor of 3M double sided.
As I mentioned before, I am a bit of a perfectionist. After a few hours of dicking around with this diffuser I would re-rate it to 7.5-8/10 out of the box in terms of overall quality. I feel now it is up to 9/10.
To the average M3 consumer it would rate at a 9/10 now.
I'm not too worried, as this is a $300 replica straight from China. I've used a lot of aftermarket carbon fiber parts on a variety of projects and I can confidently say the quality of this piece is just like everything else out there on the market; pretty good, but not perfect like OEM. I feel the same about the other aftermarket carbon fiber pieces on my car as well.