Embrittlement is often cited by hydrogen naysayers, but if they're selling cars how serious a problem can it be? Maybe they just coat their tanks with something impervious?

I mentally substitute ammonia for hydrogen when the question comes up, because it is much less implicated in embrittlement and is otherwise quite similar to hydrogen. (IANA Chemist, but I've read that ammonia actually carries more hydrogen atoms than elemental hydrogen does, at the same pressure.)