I used to be afraid to do anything remotely competitive without headgear. Now I can't stand to wear it ever, even in heavy sparring. I think once you get used to going without it, it becomes a real burden.
with the face saver headgear, the back side should cover a significant amount of the back of your head. I remember when they becoming more popular a few years back, and i think it was pro gear, that had a short flap in the back. it wasn't enough coverage to grip and hold it in place. i had a guy who spent a bit of money on it but it moved around and he got more bloody noses from it. I used one once years ago, and talk about loss of vision, I couldn't see uppercuts coming from the bar's blind spot. and i've witnessed lots of guys forgetting how to catch a simple jab with conviction, because of the safety bar. I think it's fine to use them but the boxer needs to keep excellence of skills at the forefront of their mind.
It takes some getting used to but after a while unless it gets displaced it's no huge thing for me, though when I first put one on I thought it was hurting my peripheral vision. I think it is important for young boxers to wear headgear. The headgear and the size of sparring gloves reduces impact forces and it's the accumulation of impacts that doctors are most concerned with. Even a little help can't hurt. And aside from helping to reduce facial abrasions there are nearly no chance of getting a nasty cut from a headbutt.
