I use Croakies/eyewear retainers to keep my sunglasses (and sometimes glasses) from not falling when running/at the beach/in the outdoors/etc. Or sometimes just to not have two pairs of glasses with nowhere to put the other (prescription sunglasses, prescription eyeglasses; don't tell me to get Transitions, they're not as good as dedicated sunglasses ). Do you feel it's too juvenile to wear them, even if there is a legitimate need for them? This is how they look.
???? Seems like a pretty good idea to me? I guess if you were trying to dress up for a work function they could look a bit dorky, otherwise, they're pretty functional. My opinion on most things worn, is that it is more about who is wearing it and how they're wearing it, than whether or not it looks cheap. If you're confident in something, you can pull it off.
I don't personally wear them. It's just a matter of personal preference, I guess. I certainly don't see anything wrong with wearing them.