Where do you get the "It has 4 x 250HP turbo reactors for power - 1000HP, " data from?
Right from the mouth of the inventor, in his interview, below ...
"Interviewer: Can you tell me more about how it works? How many engines are in there?
Franky: We have four engines inside, and the power is 250 horsepower each. It’s about 1,000 horsepower total."
Franky Zapata racing - jet-powered flying hoverboard interview
Some table-napkin rough calculations tells me a backpack full of Jet-A1 sure isn't going to keep 1000HP fired up, for too long!