It works, but its stability and accuracy is based entirely on how well the camera on your alt is positioned in the first place, and the terrain you're using it in. A small dip in the terrain can cause your mouse to hover over a spot thats 100 yards away. I'm sure with some practice it would work really well.

The real question is how often does this sort of AOE come in handy? Such spells are typically mana intensive, and require pulls of 5+ to really start dishing out more damage than you could other wise get spamming a direct damage spell. Potential Volley exclusion until the incoming nerf.