Those little lights probably aren't as bright as you think they are. Yeah, you can "see" them from a few hundred yards away - when you know they're there and you know where to look for them. You really want a light that's bright enough to hurt your eyes if you hold it and look at it while it's on - in daylight.
IME there are about three red tail lights that do this: Planet Bike Super Flash, Cateye TL-LD1100, and anything by Dinotte. There are probably others, but those are the ones I've seen that I think are bright enough.
I've seen way too many little red blinkies that I could barely see from 50 feet away, but that the cyclist using them thought were sufficient. I know the cyclist is there, I know the light is on, and I can barely see it. When there are no other distracting lights.