My wife has a Bell Muni with the built in rear light mount and a Blackburn Super Flea rear light. It is an outstanding setup! The super flea is bright, very compact, long run time, and usb rechargeable. The mount on the Bell muni is rugged and well designed. I don't know why more helmets don't have the rear light mount, because I don't care for the fit of her helmet on me, but I would pay $20 more on any other helmet I like to have that mount. If you haven't checked out the Bell helmets with the rear light mount you really should, I can't recommend them enough.
-Bruce