Dave wants to replace his Airport Extreme with a mesh router. Leo says that's a good idea since Apple has stopped making routers. Mesh routers are good because they are always updated and provide great coverage around a large house. The downside is that to get additional features and updates, he'll have to pay around $100 a year for that support.
Leo recommends Eero and Plume, and the Netgear Orbi. Even the standalone routers from Asus, Linksys, and NetGear have mesh features. The NetGear Nighthawk is a good one that's recommended by The WireCutter. The Synology RT2600 is also good.