I'm from Italy and i have a 3W
It's classified as L5E vehicle so:
registration: as a bike
helmet: not required ( art 171 comma 1bis CDS )
L5E is a specific category for 3 wheelers. It covers things like the Ape car and the Moto Guzzi 3 wheeler truck.
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.
Exactly correct. The low roll bars of the M3W do not qualify as a security cell (art 171 comma 1bis CDS) therefore a helmet is required. This is the advice of Borghi, the Italian importer.