Also there will be conversion kits to make your existing Vectors into Rally and to also swap the spindle between pedal bodies so you could have SPD-SL in summer and SPD in winter
yea the backward compatibility with vectors is nice. i am going to get a set of used vector 3s and buy the xc pedal body. perfect for the winter road/summer gravel bike.
MTB power pedals from Garmin
https://cyclingtips.com/2021/03/new-garmin-rally-power-meter-pedal-family-to-include-spd-sl-and-spd-models/