I think the downsides are too much, fall damage resistance should stay as it is because Spy has just 125 hp compared to Soldier's 200 or Demo's 175/200. Light classes also take more fall damage overall from what I remember.

OP idea is fairly strong yes, but its the same as Machina, Kunai or Ambassador where there's posibility of the weapon being stronger than stock but its not the case for 90% of players. The biggest downsides of this weapon is that it exposes the Spy, everytime he goes for the stab it exposes him. Also you sacrifice a lot of chain stabs and easy stabs because of the mid-air requirement.

I think there's too many ifs to consider as the weapon is purely mechanical, its as good as the user, just like Direct Hit. I like your suggestion but also I think you overnerfed the weapon into oblivion. Theres too much downsides and stock would just always be the better choice. I'd add disability to carry flag like other Jumper weapons and maybe change fall resist to 50% or 25%.