I wanted put out some feelers to see who's updated their headunits to headunits with Apple Carplay.
I was hoping to hear model specific feedback. I was hoping to retain the functionality of the steering wheel buttons and the internal mic.
Mobile audio has been a HUGE hobby of mine for about 10 years. I bought my MK6 in June, and a new stereo was the first thing that the GTI needed. I went through A nice Pioneer (brand loyalty from having used their active capable head units exclusively for years) and a Kenwood double din, but pulled them and put the OEM unit back in.
My car came with the RCD 310, and it's not that great. It distorts at 21 on the volume knob, the ipod interface is mediocre, and the features are limited, however neither aftermarket unit was good enough either. On both the Pioneer and Kenwood I had issues with Carplay (and just about every other feature). Sometimes my phone would connect, other times it wouldn't. Both unit would freeze periodically, both had screens that were far too busy and unintuitive, and I had issues with glare and polarized sun glasses hiding the screen. In the end I decided I'd rather have a free mediocre head unit than an $800 mediocre head unit.
If you use idatalink you can keep steering wheel controls and all of the other features, however, there is a catch. The OEM mic will still work, and the MDI plug will still work, but if you want to use Carplay you must run the mic from the new head unit, and if you want album info to display correctly, you must run a new USB cable. I was under the impression that since I was using the idatalink maestro that I wouldn't need to run a mic or cable, but I was wrong.
I'm in a tough spot because mobile audio is important to me, but besides the Pioneer P99 (only single din, and not super modern features) there isn't an aftermarked head unit that I'd use. I'm going to end up running a RCD 510 to a DSP to fix the sound, but that won't help with Carplay. For me that isn't an issue, I don't really want my phone tied to the car anyway, but I can see how my solution won't work for most people.
I suggest that if you decide to use idatalink with an aftermarket stereo that has Carplay to look at Kenwood. I prefer Pioneer for sound quality, but the Kenwoods will integrate better.