I thought my 505 was kind of sturdy it survives hanging out in my purse and has been dropped a few times on carpet. I also second the insurance option.
I think the main question is how does he treat paper books? if he takes good care of them he may take good care of a e-ink device? though obviously accidents do happen.
I also recommend the 500. My husband uses his and stuffs it in his backpack quite often. Not sure how it survived all those trips off shore.