I am of the opinion of full face or don't bother.

On the streets I don't wear a helmet anymore. When I did wear a helmet I wrecked bad enough that it caved in my biking helmet but broke my back. This certainly would fall into the "it saved my life" anecdote, but I don't know that I would say that actually. It may have only saved me some stitches.

I have wrecked and been hit this last year on the streets with no helmet. Once was bad enough that I was knocked out briefly, and freaked me out for a moment that I fractured my skull; but I didn't. Essentially I dont wear a helmet because I feel the trade off of my comfort, concentration and agility for the possibly illusory increase in safety is not a good deal.

In my personal experience, I feel that my serious to fatal injuries will not be avoided by some styrofoam. That they would likely be from actually getting crushed or spinal damage.

I would not presume to say they aren't a good investment and practice for some, but they aren't for me. I would hope that I am not subjected to a law requiring their use.