Well, you DON'T have to stand still to cast, you just slow down, and 1.3 seconds isn't really that long. I prefer spending 2431 magicks for 9 seconds of speed instead of 2563 for 3 seconds.
Since I use this on my magblade with no stam pool, I use this as a sprint replacement when I have to move somewhere fast. Saved me from the ghosts on multiple occasions when I was out of position in Fang Lair.