Their gauges don't use the M-Button, the M-Unit does. As for the "bus" line, that's for compatibility to the myriad of modern bikes that use CANbus. What seems of great interest to those who choose the M-Blue is the connectivity to a mobile for wireless key, gauge data, and programming.
There are some nice features, but I always prefer to have a gauge and don't use Andriod products so currently their integration to that OS is moot for me.