landing and takeoff are the main concerns with this design feature. A good example of a downward pointing tail would also be the Dornier 335 arrow, which has both a top and a bottom tail. The bottom tail featured explosive bolts as well as the rear pusher prop in the event that the landing gear didn't work, so both could be discarded. if you look at that plane, it is very high off of the ground and the plane can easily rotate without a tail/ prop strike in the back. The price to pay for this? Very long gear.

When practicality meets increased performance, its usually practicality that wins out.