rear vision

So whilst stuck at uni during the week with no real MTB trails other than the tired stair gaps to ride I've been doing fitness rides into the operahouse and back getting my kicks from the "New York Bike Courier" style of riding weaving in and out of the cars but I find it disconcerting looking over the rear shoulder when space in front is so scarce. Has anyone used one of these / has a better idea? Obviously there are the handlebar mounted but I guess with these you can just lift up your hand and swivel around quickly to pan as the area of the mirror is pretty small. That said, at least you can allign normal mirros and leave them where as with this you would have to do it every time you looked as your hands move around.

And no I don't have the money for a helmet mounted rear vision cam with heads up display inside my sunnies....(Would be cool but)