It's the batteries that make a light heavy. The lighthead part of a separated combo should actually be quite light compared to the battery. Systems like the MagicShine don't IMO need counterweighting. Especially since the majority of helmet mounts sit the light pretty much at the top of your head right at the center of gravity. There is a slightly forward weight bias since you are (probably) canted forward a little bit, but it shouldn't be objectionable. As for running the cable. I like to put the battery in the pocket of an inside layer or even pants pocket and then put the shell layer on so the cable exits at the back of the neck. Keeps cable from flopping around at your back and catching on things you walk past like your handlebars.