Due to the almost indetical design, I can't see how it would make much of a difference?
The stealth spoiler is longer front to back and will hang out over the back window about 4 inches past stock. It's also slightly wider so it may hang over the sides of the VX a little. The edges (left and right sides) are more curved towards the front of the vehicle giving a more rounded appearance that I think would complement the curves on the VX rather nicely.
As far as air flow, the underside of the stealth spoiler is pretty much the same as the VX. From what I can see, the shape of the front of the spoiler is what will direct air down over the back window. The front section of both spoilers is pretty much identical. Have you looked closely at the stealth spoiler compared to the VX?
Either way, it's still just another possible mod which is the only reason I'm posting about this. With all the VX's out there that have lift kits, Bigger tires, AC running, roofs racks with full size spares on them, I'm sure some will want to shoot for this mod if it works because, as expensive as gas is these days, not
too many VX'ers are really
THAT concerned about it