So far, I've not found any ADAS features on a dashcam to be useful, but the blind spot monitoring is a function that would be useful, if it was 100% accurate. The problem is that people who use it will start to trust it, so if it is not 100% reliable, it could be worse than not useful! If they don't trust it, then they won't use it, so it will be another pointless ADAS feature. BSoD?
I assume the DMS systems do actually reduce accidents, although I notice that the Vantrue brochure image for DMS shows a family wide awake and posing for the camera while driving along a sandy beach, wearing sunglasses. DMS systems tend not to work if you wear sunglasses because they can't see if your eyes are open or closed! Whoever tests this feature is going to have to copy the brochure and wear sunglasses...