[JulianEdgar]

The aftermarket one looks pretty good - I assume the bottom of the rear suspension arms are flush with the new undertray when the vehicle is at normal ride height.

I wouldn't worry about any holes.

I've tested AirTabs on undertrays on two vehicles; on one they made a subjective difference (giving better stability) and on another they made no measured difference in terms of airspeed or pressures. But they're cheap enough to just tape some into place at various positions and do some testing.

If the new undertray can be curved upwards at the rear of the car, that would likely be beneficial from both lift and drag perspectives.

Addition: Actually, now I think about it, I've tested AirTabs on the undertrays of three vehicles. On one front undertray they caused a great increase in vibration, presumably as the vortices impacted the firewall!