Well let's see... two of my favorite materials, leather and the elastomer that is used to make Silky, are rated 7 by Eden on the safety scale. I also have a packer made of superskin, which is rated 5. Silky is the only insertion toy in that bunch, and I take precautions by using condoms and reserving him only for times when his special abilities are called for. I also retire Silkys every couple of years.
I think how you use the toy is more important than what it's made of. A toy doesn't become dangerous just because it isn't suitable for a certain type of play. But I draw the line at toys that have an offensive smell or any chance of leaking chemicals.