Originally Posted by Game
I can't supply you with pictures, but I can advise you. Not sure wtf the installer was talking about when he said Audi windows would look any darker... all it comes down to really is the interior color (black obviously will make it look darker).
I currently have no tint on my B8.5 but I like it that way. On my B6 S4 (black with black interior) I started out with regular non-ceramic tint at 35%. I eventually had it switched to F1 Pinnacle 30% ceramic. I expected no differences in light since the 5% difference is barely anything. I was wrong, the 30% was MUCH darker than the previous regular 35%. This is because of the features of the F1 Pinnacle Ceramic itself, but it was also because their tint is as close to "black" as possible. The cheap tints you can get will often have a blueish or greenish hue to them.
That said, I loved that tint and any car of mine that I tint in the future will have F1PC for sure. The car is MUCH cooler in the sun, glare is even better reduced compared to normal tint, and it just looks way better overall since it has a naturally black/charcoal hue.
TL; DR: 30% of F1 will look slightly darker than 30% of normal tint, so keep that in mind when making your decision. I would advise going 30%, especially if you have a black interior in the S5. 15% would be more like 10% ish, which is way too dark for my taste.
Edit: shoot me a PM and later tonight I will try to dig up some pics of the 30% on my B6 to send you.