Hi there. I’m currently having a heart vs head dilemma. I want a new helmet and can’t decide between a super cool matt black or a not so super cool Hi-Vis helmet. I think the Hi-Vis helmets you can get are really good at making you noticed on the road, more so than lights in the day, but they look pretty rubbish. So what would all you guys chose, increased safety or looking good?
We have huge differences between seasons here, so I have several helmets too. I have a better looking well ventilated helmet for the summer rides and also a Hi-viz (and also a bit warmer) helmet for the dark autumn rides. And one for the rides between those extremes. Problem solved. 
There is literally nothing that hi vis can do to protect you from drivers who aren’t paying attention and/or couldn’t care less if you lived or died.
Drivers who are paying attention will see you whether you have hi viz or or not. In fact, they’ll even see you if you don’t have any lights on either.