I have clear Bourke's on my N5A, but the only reason they're there is because they came mounted on the helmet. The gap they leave is so large that they really don't provide much eye protection. I wear safety glasses routinely, and have ESS extricator goggles (the one that snap on to the helmet brim) as well, so I have plenty of good eye protection available without using the Bourkes.
I have the bourkes and ESS goggles on my helmet now, I hardly ever use the bourkes. I use the goggles on extrication and overhaul all the time and really like them. If the bourkes wasn't already on the helmet when I got it I wouldn't have them, although they look good that's about all they do.
I have the clear Bourkes and goggles. They look cool but their of no use i have put about 3 sets on my helmet but they keep getting to hot in a fire and curl up. So i don't bother to put any new ones on. As for my goggles they are so blacked up cant see out of them either.
I took my faceshield off and replaced it with a set of ESS extricators. The shield adds alot of weight to the helmet, is awkward, and just looks out of place. The goggles dont seal as tight as I would like them to but they are great for keeping dust out of your eyes on brush fires.
I use the Bourkes, and the googles on my 1010. The gap with the bourkes isn't bad. I'm an exterior Firefighter, and don't have the problem with the bourkes curling up. The googles are mainly used for car fires, brush fires, and overhaul. I do like this system far better then the standard faceshield on the traditional helmet. Best part about the googles is that i can take them off and use them without the helmet if I find reason to do so.
Well of all the responces only one person mentioned why they use other eye protection than the bourke lens. Damnthing you are correct they are non compliant to primary eye protection standards because they dont form to your face. I had the bourkes on a helmet issued to me about 6 years ago with the goggles. I couldn't keep the goggle strap from stretching out which would keep me from having good eye protection. I gave up on the bourkes looking cool and figured whats the point in looking cool if I loose my sight from bad eye protection any way. So basically it's up to you you will need another pair of classes or google that meet the ANSI primary eye protection standard.