I suppose there is some use for a jump techmarine but I can't quite picture him as needing one.
It is a cheaper way for him to keep up with the vehicles he will be patching up than a bike. Techmarines really need to be repairing vehicles around 200 points or above to stand a chance of getting a return on their investment. You can DS him next to a Storm Raven to give it some in-flight repairs. I agree though that it is a situational build for an already-situational character.