[Nexus 7 (2013) General] RunNgun42:
Having used tablets, android auto (pioneer and kenwood HU), and joying HU I think I can offer a lot of insight here.

For starters the tablet is still hands down the best carPC you can get. It simply does everything you want it to do without any sacrifices, and tends to look the most clean as well. The reflexive matte screens on android auto HU's are just dull and boring overall, but beyond that their performance is abysmal and android has been completely crippled on these devices in the name of safety. You cant reliably browse for music, the UI/search/scroll functions in the supported music apps block you from doing too much to keep your eyes on the road, and they all require you to plug your phone in which is just a PITA every time you get in your car.

I dont know about you but I dont like having a phone in my cup holder, glovebox, center console, or on some chintzy grip mounted to the dash. It's just ugly, the wires are ugly, and having an additional screen + wires dangling about just breaks the symmetry of a nice clean A/V setup. Using a tablet with hotspot is so much more elegant. The Nexus 7 will charge faster than it drains on any car accessory charging port (cigarette charger) so it should be nearly 100% all the time while you drive. If this car isnt your daily driver then why are you putting a tablet install in it? lol. Ultimately the Android Auto head units are manufactured by companies that just have no experience in this area and are prone to bugs and other anomalies. The entire experience just felt gimped.

As for Joying HU, while the concept is admirable the execution is flawed. Their biggest issue is just poor hardware. You just cannot squeeze an entire Android equipped OS with proper hardware and all the other stuff required to make a functional HU for the prices they are asking. If a tablet alone costs as much as their entire HU then imagine what kind of processor theyre sticking inside these things. While it worked overall, the dang thing has to BOOT UP every time you start your car. This might be tolerable on cold winter mornings where you might sit in your driveway for 5 minutes anyway, but for most other occasions it's just annoying not being able to get your music/waze configured until you've drive a couple of miles, or to just sit there aimlessly tapping your fingers waiting for it to start.

Also due to such poor hardware in the Joying units multi-tasking becomes a chore. CPU/GPU intensive apps like waze are laggy, multi-tasking between your music app is frustrating, and you forget doing things like split screen viewing. The only advantage these have is the ability to integrate with a backup camera, of which I have no need for since I know how to reverse my car without running over a fire hydrant.

A pioneer/kenwood HU might have superior audio internals, but you have to remember the source audio is usually coming from a streaming app which is going to be 128kbps or less anyway so youll never properly exploit all that great audio technology anyway. A simple 3.5mm to aux-in adapter works beautifully and produces good sound on any HU. I never bothered with DAC's or other ways to convert audio, just get a solid single-DIN HU and the aux-in will be fine for all but the purist audiophiles. Even among those types there is still no desire to use Android Auto since it feels like you're using a 1st gen smart phone from 2000.