Firmware
Mine came with the newest firmware when I bought it but it came from another person so he might have done a upgrade to get the new features.
As for the rebanding, they are required to switch to a channel between 851 and 854 or 855. The control channel would change in that case. Be thankful that your unit, the BCD396XT, is ready for rebanding from the factory so you don't have to go through the hell of a firmware update just to get it to work. Also you just need to change the control channels to the new ones so it should not be a big problem.