I know several people that have on-camera HMI's, but rarely use them for "newsy" type stuff because just like their bigger counterparts, they have to have time to "come up to speed"(granted, they do "warm-up" much faster though). Not good when you need to flip your light on and shoot in a seconds notice. At least in my line of work, I can't see drivers trying to get out of the track as fast as humanly possible waiting 10, 20, 30 seconds while my light comes up to temp/intensity so we can interview them when they usually don't wanna talk to begin with. You can always just leave it on while you're running around in a situation like that, but it's not ideal, may draw unnecessary attention to you and wastes battery power(and if you're doing HD, you need every WH you can save). But they are nice for fill for a down and dirty stand-up and other things. They're just not "instant-on" like a tungsten or LED top-light.