I wear the half in the summer and modular in cool weather and rain if I must. I don't run with a wind shield so, if I know I'm tourning on some 4 lane hwy stuff at 70 - 75 mph for a while, I'll break out the modular as well. Just helps with the wind. And I can flip up for bite to eat or fuel or what ever. The modular is pretty nice for me wearing glasses as well but, other than weather elements, it really doesn't provide the protection a full face would in the event of a collision.
In the middle of summer, I rarely see a full face helmet on a harley rider. But, I wouldn't tell them they shouldn't or really think any different of them for it. Now that you mention it, I'll have to keep an eye out next summer and give them the thumbs up.:cheers