This is an obsession of mine, but I'm not a professional. I dated/ lived with a Realtor for ~20mo, and I asked lots of questions about the workflow of the business.

I don't think Redfin has much of an edge in go-to-market strategy. Redfin's allows for more comprehensive data (MLS access because of membership), and Zillow's allows for scalability. Sales data sometimes show 3 months lag from time of transaction and entry into the county clerk's records which gives the MLS quite an edge itself.