I posted this here in the fall - much smaller working Jetpack, no idea if it is as far along as the Martin in terms of production though.
There are more vids of it on the channel and YT in general.
I do wonder about the practical use of these things - any engine or control failure over terrain that ISN't water, or ever from a certain height over water would = pretty assured death, I know from high angle assault courses that falls over 5m typically = huge injuries or fatal, and flying that high would probably feel "low" in one of these rigs. Fun though, but again, I'd be worried about engine failures especially, you aren't exactly aerodynamic and able to glide without wings, nor is there stored energy in a rotor to autorate - you're flying a safe once one of those engines quit I'd imagine. Splat. Or sploosh. Even sploosh you would have to get out of your harness very fast not to be dragged under and drown I bet.
I understand the attraction though, for certain. I tried one of those hydrodynamic water powered ones long ago, and was hooked, instantly.
