Sorry I thought you meant Waze - my mistake! Only a handful of apps have been signed off for full integration in-car.
I don't think many of the current generation could make much sense of it! Id find myself driving off a cliff after a couple of minutes.
Unless I'm doing something wrong but my Android Auto display didn't pickup the app - I only have Waze and GMaps to choose from.
I do like the 3D buildings on maps.
All of my android phones have had their SD cards as External, they must have been 5 different versions of Android between them all, and my old Win phone as well and I've never had a problem with that