Just adding my experience with the DS analysis tuning over the last couple of weeks.
The custom dark model seems to be working well for me. It's picking up people and cars better at night. During the day, it will often show a higher confidence for a person than the built-in model.
Faces has been very hit and miss. It sometimes works and flags an unknown (about 25%), which intermittently captures a face image (maybe only about 10% of the time). Granted, my cameras are not configured for optimal face capture.
Faces also seems to interfere with object analysis and causes intermittent crashes of BI. With faces enabled, DS will occasionally miss detecting people. Running the clip that did not trigger an alert through analysis will show that DS does detect the person, but the alert was cancelled as nothing detected.
I have object detection turned on for all cameras, I find that cuts down on false alerts due to shadows and flora waving around. The static object detection works intermittently. The barbeque on my deck is picked up as a person quite often. I don't know if the faces option was interfering with that, I just turned faces off and will need to monitor for a bit.
I played with the "Apply to motion triggers only" setting and found that DS would miss detections more often with it enabled. Again, this might have been due to faces being enabled, will need to play with it some more.