To add to this list, they also let us upgrade firmware.
For older QC35 headphones there's a 'based-connect' repo on github that lets you configure the headphones; unfortunately the newer models such as the NC700 have encrypted firmware update files so I couldn't easily reverse engineer the protocol to get all the BT commands to configure all the options you can change in the app. Actually the app didn't even work on my Android phone without GApps, so I couldn't sniff the connection either...