I'm guessing that sailing off the front gets progressively easier the faster you're going. It's the graceful landing that presents a problem.

20km/h is only a little over 12mph. I can sprint faster than that for short distances, so even if the front wheel hit a huge curb and stopped instantly, I'd likely just run to a stop. Having fallen off both conventional bikes and recumbents, I'd feel pretty safe on this thing.

Better than on a bike where you're tangled up to start with.