I use to use a bit of insulation tape myself. never had any trouble. When i got my Picasso i didn't use anything, just turned down the beam. On the only occasion i did use a defector it was on a hire van, although it was correctly fitted a was flash at several times. (lucky me)
Be aware it is now a legal requirement to have a reflective jacket in the car in case of break down.
Happy driving. fill up with cheap diesel.