Id say not safe - but looks like great fun. We have just the spot to try it here and I know just the wood duck to send up first 
surely there kites are set up different compared to normal? i tried it and id go up but then swing around n crash into the sand and it is really uncomfortable to do with a wasit harness
I flew RC planes and gliders back in the day and if you flew the plane past the up draft it would disappear behind you and not slowly .Wonder what would happen if you flew your kite to far over the back of the dune.
rc gliders/slope soarers only fly where there is an updraft aka lift? either from a cliff face or a thermal?
I flew hang gliders for many years and in the early days got blown over the back of the hill into the "rotor", which is a very violent downdraught. Very lucky to survive!
A kite seat harness is best for soaring dunes, but remember they are not designed for that purpose, and the chance of the harness failing would be very high. Here's a good couple of crossover vids.
