I’ll throw in my two cents.
I left the RSN-E to go to aftermarket on my S4 b/c I wanted some more line-out and level options (can’t remember model number, and would be irrelevant as it’d be 4 years old now). It was a very hard choice at first because I loved the OEM look. But one I made the switch I was very happy about it and never looked back. Mine had built in pandora, bluetooth, and other options. And at the end of the day, it still looked fairly OEM because most of the area was taken up by a screen just like with the RSN-E.
Anyhow, if those aren’t as big of a priority, and you’re just wanting bluetooth audio, another option would be to look into a USB powered bluetooth dongle for audio. I’ve done this in my Porsche. Basically it’s just feeding a headphone jack to RCA to that AUX/CD-Input to the radio. The radio thinks its the factory CD player actually. And it auto-pairs with my phone. So it doesn’t do the whole phone calls etc, but it does do great with allowing me to stream bluetooth audio/music to the radio.