Just got my prop guards. They do work with the Plus batteries. Good thing cause that’s all I have. I took off from my house which is 1690 meters. The RC2 had a couple warnings about high altitude detection, but didn’t prevent take off.
No.
Does anyone have any examples of US firmware blockages for other products?
Yes. Updates are used to fix problems and add features and functions. There have been no problems with updates restricting usage of DJI drones in the US.