I recently bought a used 2015 Outback 2.5i Premium. I was having issues with head unit (non-Nav, non-HK) so I decided to update the firmware. I want to provide a couple tips.
Make sure you hook up a charger to the battery so it doesn't die mid firmware update. Also make sure you have everything turned off when you have the ignition key ON, (headlights, interior lights, heater/ac). I stupidly didn't put on a charger, thinking the battery was relatively new and should be able to last during update. I was wrong. My battery died, my headunit was bricked and from then on it would just flash the lights constantly which was very annoying, especially at night. I bought a used head unit on ebay. I opted to buy the Nav unit as it they sell for the a similar price used. If you go this route, make sure you don't buy the HK Nav head unit as it won't work if you don't already have HK HU (amp and speakers are different). Watch the MFG part numbers if you buy a used HU on ebay it will say it is compatible when they are not. Also, make sure you ask the seller if the Nav mSD card is still installed. One seller sold me one without the SD card and replacement of card is prohibitively expensive.
After the successful firmware update to NU9021, I was able to fix a couple annoying issues. Primarily, my contacts/calls are now uploaded (used to fail) from my Samsung Galaxy S10e.
