Buster11 - No, the figure stated is 250HP each - not 400HP. I, too, am skeptical of even the 250HP figure, and I'm thinking the standard poor level of journalism has mistranslated the power ratings.
I cannot imagine where it would require 1000HP to levitate and accelerate a human body.
The Martin Jetpack propels the operator with a 2.0L V4 piston engine producing 200BHP, and appears to provide a similar level of performance to the Zapata Racing version, with its 4 "turboengines".