They are essentially co-investing with the buyer and renting them the property. You pay the property off little by little and when it is sold you split the profits.
The idea is really interesting, but there are a lot of questions still yet to be answered. How much will the premium be for renting the property and what happens if the property is sold at a loss? What is the split then? My guess is there's no risk for this new startup if there is a loss.
This idea might make sense in areas where housing prices are out of control.