I'm doing Rx right now and like someone on reddit said, FA in question form (which is what Rx is), is just different from Zanki, which is FA in flashcard form. It's really been another form of spaced repetition (especially since I've been doing it on random) and active recall, which has been synergistic for solidifying my knowledge. Also, it's one thing to know something, but it's another to apply it to clinical scenarios, which Rx has allowed me to do.
I say this as someone that was seriously considering foregoing Rx at first because I thought it would be redundant, but it's been helpful and I'm running through Zanki even faster now. I'm aiming for 10,000+ qs as well.