More efficient than traditional construction by hand, sure. But why on earth would you use a 3d printer to print individual houses when you can just fabricate pieces and lift them in place with a crane?
If there is an advantage to building on site, then a mobile fab in a trailer, but molds, prefab walls, are much, much better.
I am much more excited by panels being produced in a factory with a waterproof/fireproof layer, insulation, structures, these are fundamentally better than just squirting out concrete. You can see demos of houses that fold out, or just panels that are assembled onsite. Either way, I don't see that the printer is all that efficient. Yes, it prints fairly fast but you have to move it to each new house. Whereas if you have a factory, you can crank out modular panels 24 hours a day and ship them.
It doesn't seem to make sense to build entire modules though, unless they are all identical, like on a ship or prison. Because the modules are typically big and bulky to transport. And the form factor means you have to limit the size of rooms according to the geometry of the container. But mass production of standard units that are assembled like Lego, that seems way, way better. My favorite is when the article talks about a chinese printer bragging that it is using industrial waste in the concrete -- just what people want to live in close proximity to...