My opinion would be that they are good for people that are not that good at the game, but they are not something to invest in if you want to improve.
They do give you some increase in accuracy, and they might increase your K/D ratio - however, relying on them is a bad habit to get into.
Eventually you will get as good as people are with FPS freaks, if not better.
I just personally think they are horrible. A good idea, but not a good investment.
//AC