"The rider's and jetpack's center of gravity are well below the thrust planes of the nozzles which ensure fore-aft (pitch) and side-to-side (roll) stability," claims the Jetlev website.
What about the water jets themselves? Those look like they could cause some serious damage; however, the jets actually operate at relatively low pressures of up to 60 psi--nowhere near the roughly 2500 psi operating power that of the industrial pressure washer you might use the clean vinyl siding. Jetlev does warn to keep hands and arms clear of the spray, but incidental contact isn't likely to cause serious injury.
In fact, the flow-rate of the water streams produced by the R200 act as a risk limiter in the sense that, once you reach about 30 feet, the thrust won't carry you any higher. That, coupled with the 33 ft supply hose length will keep you from accidentally blasting off into the stratosphere. And, if you were to fall to the water from 30 ft high, Jetlev notes that you would be entering the water at speeds of less than 30 mph. That's about equal to a 10 meter Olympic platform dive--indubitably perilous, but not certain doom.
Obviously, proper training, physical ability and practice are needed to safely pilot the R200. But, if given the chance, it would be an experience hard to pass up.
Click the image below to watch TRANSLOGIC 62: Jetlev R200: