What is cool about this document is that toward the end it references further tests outdoors of the jet-platform.
Since reference 1 was published (1953) flights on a jet-supported platform were made out-of-doors. Figure 10 shows a typical flight on the jet-supported platform. The riders of such a vehicle had practically no difficulty with the wind. In calm air the rotor-supported vehicle hovers more steadily than the jet-supported vehicle. In gusty air the rotor supported vehicle was more disturbed.
“Typical flight”, far from being a mere experiment, in the three years since the first trial, the platform had become almost a method of testing jet concepts.
Notice in Figure 10 below that the platform size has shrunk to foot width and the support legs are compact and protect the jet from the ground, naturally.
The notes in this document referencing the jet-platform:
3. By comparison with a low-inertia jet-supported platform previously tested, the teetering-rotor-supported platform flew steadier in calm air and with larger oscillations in gusty air.
4. Although a substantial inertia of the machine did not appear to be particularly critical, an arrangement in which the flyer’s body moved with the flyer’s feet was physically easier to fly in rough air.
Link to full PDF file of NACA RM L54B12a