Regardless, we ask for the address as well as zip because in many areas, a ZIP is not sufficient to gather detailed data, as an official may represent one part of a ZIP code and not another.
Politiwatch, the non-profit that made WhoAreMyRepresentatives.org (https://politiwatch.org), is purely public benefit. We're trying to promote government transparency and political fluency. Nothing nefarious going on here. You'll have to take my word for it, though. If you're still feeling paranoid (and rightly so), enter your neighbor's address.