The feature that tells how many amps are being used by the trailer
brakes -- Just sitting in the driver's seat, without a meter or complicated wiring, nor opening any connections, one can read the numbers and do some diagnostics -- May never need it, but it would pay for itself first time one did, IMHO.
There may be other troubleshooting features, but that one alone would be a deal maker for me.
Nothing wrong with Prodigy, just that the P3 has more.