Good article about the Z1R (here's some related links):
http://www.webbikeworld.com/z1r-helmets/z1r-zrp-1.htm
http://www.motostrano.com/z1rzrsohe.html
Original article:
http://www.motorcyclistonline.com/gearbox/motorcycle_helmet_review/index.html
If this is true and the Z1R is that good (and I'm looking for some more studies to back that up/convince me) then it's all the more reason to (1) never buy used and (2) buy a new helmet every 3-4 years. EPS foam starts to break down over time, so time is an enemy as much as "unknown condition" of anything used.
I still maintain that using a used helmet is one of the absolute stupidest things someone can do. Probably better than no helmet at all, but only marginally so. My intention is not to undercut this guy's sales attempt here, but let's be serious - a used helmet? Are you kidding?
Helmets are not the place to skimp or try to "get a deal". I firmly believe this. But it's your brain, your choice.