It would probably be alright for abrasion and sliding and better than nothing in an impact, but of course, not as good in an impact or slide as a super-duper expensive Arai or Shoei.
My daily wear is an Old-Style Davida Classic. Meets no Safety Standards anywhere in the world. However, it's the most comfortable helmet I own and its construction is top-notch. Would do well in a slide, but only so-so in any kind of impact. Having said that, 90% of my riding is bopping to and from work and around town where speeds are low, I live in a rural area with nearly no traffic and few cars, and I'm a gambler that's playing the game that say that statistically, most motorcycle crashes involve some sort of slide while very very few involve an impact with a unyielding object. However, if the object or impact is hard enough to f--k me up past that layer of fiberglass, cork, air-space and canvas webbing, then the impact would still jack my spine just as bad as wearing a gee-whiz wonder helmet.
Would I like to have a 700 dollar Arai and Kevlar armor coming out my ass? Sure, but I, 1: can't afford it, and 2: it's hot as HELL here 6 months of the year and all that armor and clothing would SUCK to wear. Big issue: I'm not going to dress up like an astronaut for a trip to the movies since I don't like walking around looking like a damn Power Ranger and part of these old bikes to me is the proper look. Armored jeans, Rocker jacket, Pudding Bowl helmet, flight gloves and Jungle Boots or over-the-ankle Classic sneakers, FOR ME, are the right look, and they give me the protection I will need considering my riding location and style.
However, I do have a traditional 3/4 helmet and a full-face (though not a big $$$$ one) for different occasions.
I don't buy that unless your stuff is new or full-face or DOT/Snell or whatever approved that it's akin to wrapping your head in tissue paper. So all the GP racers who wore the Low-Dome helmets were dumb#$%*s who were wrapping thier head with little more than a towel? All the riders up till now that wore the helmets in the 70s and such were not protected? Of course not. Has the technology improved? OF COURSE, but older helmets are not as useless as people make them out to be.
So yes, I have no problem with old-style gear. Old gear, OTOH, should be checked for safety and life left, but if it checks out, go for it. New stuff made to an older style, I have no problem with.
