Thre are a lot of full scale and models with flat stabs -- other than needing bracing to keep from going the wrong way when the elevators are deflected -- they work just fine
for years I felt the nice curved stabs were superior - and for being "clean" yes they are -however- as far as how the plane flies-- I will bet money that is a carefully done comparison test - you can't find any differences --in models such as sport models or aerobatic stuff -