Main issue is that it doesn't boost your Reaction, so you're just as easy to shoot, until you throw some Combat Sense in the mix.
Just for the record, you're normally better off with an Increase Reaction spell instead of Combat Sense, if you can cast it at an appropriate Force to handle the augmented attribute.
You've got
much less Drain to worry about, it's a flat addition to Reaction for everything (so skills, too, for instance, not just surprise/dodging), and opposed test rules for Combat Sense being an Active-Detection spell. Heck, just to cut down on the die rolling alone, thanks to it not being a Detection spell, it's worth it, in my opinion.

Unless you've got a fat bonus on Detection spells from a Mentor Spirit or focus or something, Increase Reaction's the way to go.