I got a round mouth piece for my 901 today and let me tell you I will NEVER use the flat kind again. This thing dont leak!
I got the Dura carts today (round mouthpiece) and I don't like them at all. I prefer the flat. Easier draw for me with the flat.
That's funny - I prefer the flat mouthpieces. Not because of any e-liquid issues but because I don't like the feel of the round mouthpiece.