If upgrading it doesn't increase the time it can be used above six seconds, why is it upgradeable in the first place?
When I was playing around with it in PvP the opposing side could see me move, doesn't this sort of defeat the point?
I'll still carry on using it of course. It's lots of fun to speed around maps popping in and out (helped by the nice short cooldown) and the tinkly sound it makes is very pleasing to the ears.