Helmets with break-away visors.
 

Or, more precisely, the break-away visor that some helmets have (sorry, can't edit subject lines after posting them).
I've been considering the Kali Lunati helmet specifically and noticed that it features a "break-away" visor. This phrase is new to me and I'm wondering if it facilitates unlimited removal/replacement with the original visor, such as if my desire changes with my mood or, if this visor instead becomes damaged when you remove it and can only be replaced with a new visor.

I think a break-away visor is designed to come off the helmet during a crash and reduce the rotational impact.

Many, but not all, mountain bike helmets have removable clip on visors. I guess they would break away on impact but quite frankly, if I'm about to face plant, I'd prefer a rigid visor to help mitigate the impact.