I received my Echo Auto today, and am using it in a 2012 Chevy Tahoe via the auxiliary input. I was really impressed with how well it understood my commands, and most stuff seemed to work very well as expected. I have found two things so far that give me slight pause with a 5 star review for my use case.
1) I have an Alexa controlled Garage Door opener, but when I tell Echo Auto to unlock my garage door it tells me it's not supported to unlock a door from Echo Auto. While I understand the security concern with it, you already have to give the Alexa App a pin in order to unlock a door via the app, so why can I open it via the app (my phone which is much more likely to be stolen/lost) but not via the Echo Auto?
2) When using navigation via Echo Auto, I was able to make my iPhone open Google Maps thanks to the configuration feature in the Alexa app, however, both with Google Maps and with Apple Maps, you have to "tap" the notification icon in order to open the maps icon, and then in Google Maps at least you have to "tap" the "start" button in the app. To me, that defeats the purpose of "hands free" operation. I mean I guess it's still easier than scrolling through the phone for the app, and typing in or hitting the microphone icon to specify an address, but not by as much as I hoped.
As for integrating with audio apps and other smart home features, it seemed to work really well, so kudos for that!