I'm thinking of using the Cygolite as a helmet light after Geoman replaces the MS battery, if that ever happens. I've had two instances where the MS battery went dead over night while plugged into the light head, with the charge indicator on yellow. Geoman says to unplug it at night, then plug it back in in the morning, which kind of sucks. Riding to work with my old Bell headlight definitely doesn't cut it anymore, so having two bright lights, one for backup, seems like a good idea to me.
As far as the mounting of the Cygolite goes, yes it does sit more in front of the bar than on top of it. I don't use a bar bag so I can't comment on interference issues they might cause.