I have been playing the Warburton Arturo Sandoval 3C cup with a 7* backbore (also a Mount Vernon clone) for a long time, but wanted to try this Austin Custom Brass Mount Vernon clove for comparison.
However, I can neither, feel or hear even the slightest difference. The cups and backbores look identical, although the throat may look slightly, slightly larger on the Austin Custom Brass.
I A-B'et it (blindly) with two friends, and they were unable to spot any difference.
The Warburton Arthuro + 7* backbore costs 111€+66€=177€, and gives you the option of changing the backbore.
The Austin Custom Brass MV 3C is 121€.