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Now, to the question. The R7104SB RX is fully compatible with the 12FG. It does both FASSTest (telemetry) and FAAST (non-telemetry)
The 12FG does FASST and will work with the R7104SB. Your servos will work fine with it. You will have 14 ports, 12 fully proportional and 2 DG ports. Plus S.Bus.
R7014SB.pdf