I thought I'd have a bash at using the (EXPERIMENTAL) Vertical Swing Meter and with hilarious results.
It's not surprising most players defer to the horizontal meter while a few choose the 3-click.
There's several glaringly obvious problems with the vertical swing meter in it's current state.
1. It appears right in the middle of your screen obstructing the view!
Solution: The best place for it would be on the right hand side of the screen. This would allow for a clear view when taking a shot and players can still see the meter clearly.
2. The swing on the Y-axis is counter-intuitive (push away from user and release) and the meter runs from top-to-bottom!
Solution: Change the swing meter to drag towards user and release and have the meter run from bottom-to-top.
These are simple solutions that will dramatically improve the meter.
Obviously a new meter takes getting used to and it will probably still take a bit of work to convince players to move away from what they're used to but at least these changes will keep things moving in the right direction.