Depends on the use application. For observing especially large objects[1][2], I agree, it would be very hard to use for anything beyond a quick demo. But on the other hand, I think the phone is a perfect viewport for on-the-fly smaller applications, like an AR measuring tape[3], adding info about artwork in a museum, displaying a virtual prototype of a dish on a restaurant's menu[4], translating street signs on the fly[5], etc. The phone is perfect for applications where you don't want to plan ahead or be constantly carrying an extra piece of equipment around.