I use IVS (line cross and intrusion zone). MD is not enabled. Works well.
I record 24/7, not just when an event occurs. Disc cost is low, compared to missing something because IVS (or MD) didn't trip.
Secondly, if IVS on cam #1 triggers, I like have recordings from cam #2,3,4, etc. (which didn't trigger)
I have strobe lights set up, they go on when there's an IVS event. Works well.
Instead of struggling to make sure that "Record on Event" is rock solid dependable, consider recording 24/7. The when viewing Playback, check the timeline for the orange IVS events. Just in case you worried that recording 24/7 would require you slog through hours and hours of recordings to find events. (ie: just in case you thought that was the benefit of "Record on Event")
For me, there is no benefit for record on event. My 2TB drive stores 7 days of recording from 6 cams, all 24/7 recording.
Fastb