1) A. light weight B. improved aerodynamics C. ability to switch between dynamo & battery as power source D. ability to charge battery with dynamo E. variable focus on light beam
2) Weight of battery and complete use of water bottle cage
3)Good light output even in cold weather and durable battery
4)Yes, by turning my head I can give motorists clues of my intention to turn or change lanes(in case they miss my hand signal) and at big intersections to further alert right turning motorists that I exist. Also it is great for shining wildlife along my route.
5)My bike is stored in a locked basement at work so those aspects don't apply, but part of the reason it is in a locked area is because I do fear they could apply.
6) I would hope 30W on my handlebars and 10W on my helmet would. In deed, I count on it.
7) On level stretchs, yes. On the chunk of downhill that I hit 34 mph on in daylight, with a sharp turn midway, no; I slow down to 24.
8) Cost
Satisfactory illumination
Size
Visibility to motorists
Maintenance free
Environmentally friendly
Appearance
Theft proof
9) Nite Hawk dual+auto charge & Marwi Nightpro helmet mounted