if they bough more than a year ago then they've got a decent amount of equity...
For me, interest rate risk is the biggest concern.
Also.. I wonder if there are now enough builders with projects in the ground that the supply/demand imbalance may start to lesson over the next couple of years. It's taken a long time to get enough electricians/plumbers etc needed to start building a lot more homes each year... eventually there will be enough tradesmen and we'll be able to build a lot more units of housing each year.