I wouldn't mind using both.

What I REALLY want is a brake-actuated brake light. Drivers can't tell if your pedals are moving at night, unless they're close enough to illuminate your pedal reflectors and notice them-presuming you even have pedals large enough to accommodate them-which doesn't help for anyone rapidly barreling up behind you, and it takes too long for motorists to register rapid deceleration by depth perception of my running lights.

A brake light isn't going to be misinterpreted by anyone.

Seems like it should be easy enough to rig, at least on MTB style brake levers. You would just use a relay on the brake lever to turn the brake light circuit on when the contacts are separated. (One contact on the brake mount, the other on the lever. You apply the brake and the contact is broken, light turns on.)

I figured a product like this would be widely available, but I haven't seen one. Been considering rigging one up, but my handiwork is always kinda gruesome.