I've never seen a magic shine come at me before, but have seen some P7 flashlights in action. The bright setting is NOT too bright for riding in well-lit parts of town here with lots of traffic. Are they annoying? Sure, but they are not "blinding" unless you point them DIRECTLY at the oncoming driver's eyes. Most people here with P7s try to use the dim setting in neighborhoods and such.
My philosophy right now is that it is too bright if it REALLY blinds them, or makes them see spots. Lights that are annoying are good, when you are trying not to be dead.
Once my main light dies, I'll be getting a magicshine, though. Motor vehicles turn in front or on-top of me almost every night on my way home from work, and I run with a 80 lumen light on the handlebar that is pointed directly at windshield height, and a 80 lumen flashlight strapped to my helmet that I use to see the road and/or to flash directly in the face of people coming from side-roads and/or driveways. I may replace the helmet light with a Q5/180-200 lumen light sooner than that (takes AA batteries and lasts 2-3 hours on a single charge), since it suddenly started eating even new rechargeable batteries a lot quicker than it used to.