From where I'm sitting the red rear LED blinkie is the easiest light to make effective, long-lasting, small, and cheap. For purists that need just that one special GOOD blinkie, there will always be helmets without blinkies, or hey, use both, one more light can't hurt, can it?
But I guess that's just because I have a different theory on good blinkies. My theory is, there may be ways to make a blinkie excellent, I don't think there's a way to make it bad. Or at least I've never seen a blinkie cheap enough or chinese enough to not still be effective.