[Android Head-Units] hippelsepp:
Hi,

I think that depends on your definition of "problems". My definition of a real problem is when there is no solotion on xda developers :)

OK, first I would recommend that you buy a head unit that was made for your car brand and model if available. I own a 2013 Skoda Rapid (similar to VW Polo / Golf, no "dirty" jokes please lol) and bought a VW specific model ("Autopumpkin" (reseller) 2 DIN for VW, RK3066 processor with Android 4.4.4 @ 800x480px, firmware is KLD2).

Installation: Plug in the quad lock CAN bus and the head unit was ready. Nothing else to do.

AM/FM:

In some cases, your car antenna needs +12V power to work properly. My head unit has a "phantom power adapter" (don't know if this is the right word in english). If you don't connect +12V to antenna, the reception is awful, I only received 4 stations with poor quality. Once the pantom power was connected (in my special case, I also needed a FAKRA adapter to connect the head unit with the car antenna since the plugs from the head unit didn't fit in the car connector), I received 18 stations (more can't be saved) on 88-95MHz (band goes from 88-108 here) using auto scan mode.

"Doesn't need to be rebooted":

I don't know exactly what you mean, would you like to specify that? The head unit can't be always on due to the high power consumption which would kill the battery very fast. Boot time is about 20-30 seconds but it remains about 5 minutes in standby if you pull out the ignition key.

Sound quality:

If sound quality is as important for you as for me, you MAYBE have a problem with those cheap head units but that also depends on what you like to do and to what kind of music you do listen.

On FM, sound quality doesn't matter for me because I use FM only for traffic announcements and news / documentary). The built in EQ is not the best one, at first I was thinking about to send the unit back because of the bad quality. After some days, I tried Poweramp with it's EQ and the difference was HUGE. Sounds better that the original car radio. Later, I tried Viper4Android (EQ app) since the Poweramp EQ only works for Poweramp and I thoght better radio sound quality would not be bad, but AFAIK AM/FM (and Bluetooth) sound output is not processed in Android what means only the build in EQ can influence the sound quality of that parts.

Traffic announcement (TA):

But one thing about TA feature does really drives me crazy: If you have enabled TA and the radio app detects traffic announcements (what happens also if the radio is in "background" respectively not explicit opened), a "modal popup" appears and you can't do anything (you can't skip TA or switch to another app) but vol up / down or disable TA with the "Close" button at all what means that you have to go to the radio app and enable TA again manually.

Bluetooth:

Bluetooth works much better than expected. If I get into the car in the morning, my phone (Sony Xperia Z2 with stock rom) connects with the head unit in seconds. If I press the "Play" button in the head unit's bluetooth app, it almost instantly continues playing my Spotify playlist from the phone (Spotify app doesn't work on my head unit, don't know why...).

3G / Wifi:

About 3G: Sometimes the HU loses connection because the power supplied by the USB ports is not enough. In that case, I have to power off and on the unit again (but "soft" reboot, done in seconds). Wifi (if you use your smartphone as hotspot with teathering) does work very well but not on distances over approx. 10 meters.

About GPS:

The GPS signal fixes very, VERY fast (2-5 seconds, but thats maybe because Android fixes the signal at boot time) and the supplied navigation app (iGO Primo) can calculate a route from south germany to a random forrest in Poland (I tapped on a random place on the map)	approximately 1500km away in less than 10 seconds.

Dual way CAN bus:

Does work with my car, I can control radio stations via the buttons of my on-board computer / MFD (Multi Function Display as called by VW, my car doesn't have SWC) and the MFD shows the station frequency. I can also control the Media Player App (next / prev track, not volume), but only the built in one, not Poweramp.

Conclusion: If there is a HU for your specific brand / model, you should not have as much trouble as if you buy a generic one, especially with installation. You should have at least some basic Android, car and technical knowledge and (most important) the will to play around with your device, try out new apps, firmwares and roms, play with the settings etc... If you want a real plug and play solution, you maybe have to pay 1000€ / $ +. You get what you pay for :)

I hope my reply was helpful.