At the fuel flows they are using, the explosions aren't that much of an issue. These look like wisps of hydrogen and oxygen in a vacuum chamber, not a big jet of fire steaming out of a nozzle. The detonation wave doesn't look like it is contacting much of anything.

They have a sustained rotating ring, a detonation chasing itself around a circle. That's great, its more efficient, but it is a long way from a working engine. They need a properly shaped chamber, a nozzle, and a few other things before they can test for the expected increase in ISP.