As long as you have an "s-CPU" unit (Serial number begins with 61xxx), the ADS-B box will work and will provide the weather features. Those features have not been developed yet, but they will include Nexrad, Metar's, TAF's, TFR's, winds, lighting...etc. The FIS service is indeed free from the government. When it is all up and running across the country and the software is finished to display the data on our EFIS, there will be no logical reason I can think of to go with XM...