From what I gather, bump keys are keys which perform the same basic function as lock picks. They're cut with a "generic" pattern of nodes and notches and the user "bumps" them to make them work in individual locks. I can't imagine any legitimate use for them. The website probably hides behind a "they're for the locksmith trade" rationale, but any locksmith could make the same thing for his own use in less than a minute for next to nothing.