Thanks for the link. I hadn't heard of that site before and it's definitely awesome. At first glance, they appear to focus on HPD data specifically for the purpose of examining housing and landlords as well as piercing LLCs. We pull a wider array of data in an attempt to cover various types of properties—residential, commercial, condos, etc.—and to enable different types of analyses such as via our explorer map. We also have a native iOS app that's quite useful when you're on the street.

They have some really cool features though. I'm going to dig around.