If he has already rooted miui with vendor mounted twrp, then there's no need of lazyflasher. Custom ROM doesn't need lazyflasher..Lazy flasher zip only needed if we are flashing twrp on the miui or if we are flashing miui via twrp. We don't need lazy flasher zip for custom ROM. Am I right?
Also he is has already rooted miui ROM, this can be done only via vendor twrp. Right?
Sry if my answers were misleading..