Hmm, as someone who has spent a fair amount of time in the hills (Scotland rather than Cumbria, but the terrain is similar) I can see this might provide some limited usefulness where time is critical (Heart attack, serious bleeding) to stabilise the casualty until the SAR/AAmb team can get there, but as others have said, getting the jet pack to the nearest location to the casualty will take time. I had a friend who had a heart attack on the hill, his friends did (unsuccessful) CPR, but having quick access to a defibrillator might have saved him, but they were 10 miles from the nearest road.
Most MRT callouts are for minor non-life threatening injuries or lost walkers (and drones are great for the latter).
I also doubt it's usefulness in more mountainous terrain - you're not going to use one of them on a crag for example