He's getting volatiles leaking from the connection between the main engine and the oxidizer tank. That's really bad. See the video from :53 to 1:02 or so.
I'm sure he knows that. I am in no sense an aerospatial engineer. And I appreciated the video, BC. I give this guy (and everybody else trying to drop the cost of spaceflight) my full moral support.
I just think that he's got a ways to go before he mounts that engine on a vehicle.