I just bought this upgrade a few weeks ago and it has already payed for its self. This is a very good addon to any gun. It increases the consitancy of the shot to shot velocity. It also makes the gun much more efficent. You can get many more shots out of each tank with it. Plus it will keep the velocity much more consistant.
It is a good cheap upgrade that will pay for its self after a few games so buy it if you can afford it.