I like the double, and I do know someone who lost a motor that had a spirolox fail, not clear if it broke and fell out or fell out and broke. It was a single. That said it seems like a rare occurrence, if your stuff is all set up and ready to go I wouldn't be afraid. I really don't see how those things could just fall out.

The guy who had the failure had a setup that was hard to keep from detonating too, and I always suspected it somehow may have caused it.

Now I need to pin those needles, got to feel that heat
Hear my motor screamin while I'm tearin up the street