This article shows that most modular helmets can meet snell standars. they just dont test them..


http://www.motorcyclecruiser.com/accessoriesandgear/flip_face_helmet_comparison/

Flip ups are more for convience than vanity or air flow issues.  It's nice not haveing to take off your helmet when you enter a gas station to pay for gas, run in the bank to make a quick deposit, feel like haveing a smoke, ok just flip up the front and smoke.

I like mine.. I have a Fulmer. I LOVE it in the summer when I can stop at a red light and flip it up to get some air. Also like above.. its nice to run into pay for gas and to get your sun glasses on/off  I love it. I wouldnt buy another type of helmet ever 

I am using a Vega Summitt 2. I like the flexibility.  It gives me much better visibility flipped up when getting the bike into the garage at home, and navigating the parking garage at work.  Also nice getting gas, sitting in traffic, things like that.  I guess I will continue loving it as long as it is not the cause of my death.  If that happens I hate it.

Regards
Graham

I own a Caberg Justissimo(flip-up) and a Vega Montery(full-face) I use the Caberg flip-up for around town driving and running errands and other times when I know I'll be on and off the bike fairly often and speeds will be fairly low. I use the Vega full-face for longer distance rides and especially freeway riding. This is also because the full-face helmet is substantially quieter at higher speeds.

I wear glasses too, so taking a full-face helmet on and off is an extra ordeal that really requires 3 hands.

-James