I did a similar thing when I was in the market for a new house. It was ugly and very hackish, used as many of the built-in filtering features of the sites I was scraping, but did a lot more filtering in post processing. It really bugs me how so many real estate websites don't let you filter on arbitrary fields. Faceted search has been a solved problem for 20 years ...
It’s been useful for finding new places for myself and my friends - we can usually get tours before the properties are posted on Zillow.
Though definitely against a few privacy policies