The standard M3W roll bars are head-rests only. They help against an impact from the rear but not much in case of a rollover. The Australian version makes more sense (but does not look that nice).
A full face helmet fits well to the Slingshot, for the M3W a classic style helmet with goggles is the way to go.

Hannes
once: Green M3W; 2013
now: Red 4/4 Sport; 2011
and some practical cars for use in real life