In a very simplified nutshell - yes. HAR is the MLS in Houston, and Redfin is a brokerage in Houston. That allows Redfin to sign an agreement with HAR to access

In a very simplified nutshell - yes. HAR is the MLS in Houston, and Redfin is a brokerage in Houston. That allows Redfin to sign an agreement with HAR to access their listing data and show it publicly. HAR will have 100% of listings from participating brokerages (non-participating brokers are a very, very small percentage). Now, as long as Redfin follows some rules they'll have no problem keeping up to date listings (after all, getting them directly from the MLS is the best source you'll get). Zillow, on the other hand, has an agreement with some MLS's, but for the most part they rely on alternative methods of getting listing data. The only reason that have any (IMO) is because they have consumers looking for property there - which gives the Realtor incentive to upload/update their listings. So as everyone else is saying, Zillow can fall out of date - whereas Redfin can actually get penalized for being out of date.