A long time back on Oz TV one particular soft drink maker (whose product is renowned for cleaning pennies ) ran a lot of ads featuring this type of adventure. I don't think it is particularly dangerous or for my opinion very exciting once done. (explained by the "olewill' signatory)
Looks fun, I'd give it a go. I've jumped into the sea off cliffs from that sort of height, so no worries about falling off provided you ensure the rider stays well clear of the boat.
I'd probably prefer to do it from a charter boat just in case of damaging any of the gear
Anchored by the stern. had 2 poles set with guys with the sheets running through the ends, this gave altitude good control as you could 'kite' the spi.. Lots of fun and no injuries.