Welcome to the "light side".

Drag is a non-issue. My Schmidt eDelux has an ambient light sensor that turns it on and off. There is no noticeable difference simply because I've gone under a bridge and the light turned itself on, or when I come out and it turns itself off. My Luxos-U has a bar-mounted remote switch. I feel no change when I flick that light on manually either.

Weight, well I know NC is hillier than the ancient lake bed where I live, so it may impact you differently. But still, it's no more than a second water bottle. (And if I had a dollar for everything on my commuters that weighs no more than a second bottle, I could afford a coffee at Starbucks.)

Be advised, the Luxos-U is not completely waterproof. If water gets into the jack where the bar-mount thumb switch/USB port plugs in, it effectively becomes a disco light show until it drains its battery and the jack dries out. It helps to run the wire down under the light, then back up, forming a drip loop under the light. Unplugging the remote switch and using the rubber plug is not an effective countermeasure, since it doesn't fit tight enough to prevent wicking water in. What I've found it that leaving the jack open--nothing plugged in at all--works best in the rain.