Another disadvantage is the way it shortens the length of your overall battle line, which reduces the opportunities for envelopment. I like a nice envelopment when I can pull it off. Also the AI doesn't always cooperate and march right into the killing zone of the "V." Still, it's a neat idea when it works just right.
Thats the major dissadvantage as far as I can see, yes the guns in a V do have a tendency to shoot up your line, but I dont mind the micro manage involved in stopping that. However, if you are trying ensure there are no survivors that will pillage your lands after the battle, an envelopment is the best way to go. The V doesn't really allow that.
While it is true the AI doesnt always cooperate in running down the funnel, this tends not to matter *to* much, as I mainly use it as a way of protecting the guns, while ensuring they can fire as much as possible. So long as the AI doesnt outflank me, its all good.