The basic rearview mirror on the US GTI is very basic, like just a mirror that can swivel basic. But there is an option not offered by default that can be added after the fact. The mirror glass goes to the edge, its auto dimming, has homelink (garage door opener) and a compass.
The installation isnt technical but I have to warn you, getting the A-Pillar cover off is a pain in the ass and many report breaking clips. And you do want to do it correctly and be careful because thats where your side curtain airbag is. You can find the directions here: https://www.youtube.com/watch?v=vRzV4vKY1r4 This video is also made by the website I purchased it from https://www.shopdap.com/
There are lots of different versions of this mirror that depends on both the year of your GTI (or other VW) and its options. Here is a handy pdf explaining which model you need for your car. www.carworklog.com/stuff/Manual/HomeLinkMirrorMatrix.pdf
I myself have a 2016 GTI SE and no DAP so the version I purchased was 000072548C.
Original on the left, new one installed on the right.
The auto dimming feature works well, better than I was expecting. Its pretty quick reacting and really cuts down on glare of headlights in back of you.
The homelink (garage door opener) works great but make sure to follow the directions, its steps are very specific and you do need to know the version of your garage door opener. Included in the kit is a card that has a QR code on it with video directions, I highly suggest watching this before setting it up.
The compass is a compass, it work once its calibrated, also explained on the card included in the kit.
Overall this mirror a great addition that looks and functions way better that the provided one. Highly suggested.