I have a 2018 MS.
Can someone tell me if the USB ports for the rear seats just for charging or are they proper ports that support playing music?
Just for charging.
The rear USBs do supply a bit more power than the front ones, so the rears are slightly better for charging. If I remember correctly when I tested them, the rears provided about 20% more power. @EVRider is correct.
As other posters have already written, the rear-seat USB ports are "proper ports" for charging. Music support is not a requirement for a USB port to be "proper".
Does this even work with the front one?
Do i have to install a certain app on the phone for this to work, i'm on android...
@rothman - no app is needed to charge your phone from any of the USB ports in the car.
Now to play music from your phone, you'll need any music player app and connect via Bluetooth. UBS music is done by having a USB flash drive with music such as MP3 or FLAC stored on the drive. No app or phone is needed.