Drag has various forms, one of which is induced (or vortex) drag. Vorticies predominantly form at the tips of flying surfaces such as wings and tails so having two horizontal tail surfaces ( and therefore 4 tips) would effectively double the induced drag produced by the tail i guess.

But would this be noticeable? I doubt it!

I can't see much in the way of an advantage from this setup, and all flying surfaces are prone to flutter if not done properly but having said that it would look a bit different wouldn't it?!

- Martin