It’s a very interesting clip. Pay close attention to his mic technique in particular. He’s using a Shure 545SD or SM57 in his left hand, with the harp on top. He keeps the mic very close to his mouth at all times, tilting the handle down when he sings so he can address the mic from the side, tilting it to horizontal when he plays to address it straight in with harp in front of it. Very efficient and effective.
Mechanics matter a lot when you’re looping. One of the biggest potential problems is taking lots of time to switch from one thing (like singing, or using certain FX) to another (like playing, or using certain other FX)–it makes the performance seem slipshod, and it gets boring. This technique is designed to make switches from one thing to another quick and seamless. It begins with the mic selection (which is chosen to flatter vocals as well as harp) and includes the physical positioning of instruments and hands. It’s all visible in the video, and well worth studying.
Pretty smart guy, that Son. Of Dave.