I really love my directional shields but you NEED to get the first upgrade, which stops it from draining shield power for using it (it's only 1k so it's not going to break your req points)
Although I do wish there were a way to bind keys to which side you wanted the shield on. Also, it does make a difference to the amount of shield you have on the active side. It will make the active side blue, which is a stronger shield.