I smack my kids.
However, I think the absolute essential point of ANY discipline method that you choose is that it needs to be accompanied by teaching, administered in love, and applied consistantly! Your children must understand that you are not venting frustration on them (that's abuse!) or getting your way because you are bigger, or they have pushed you beyond the point of being reasonable, or whatever. When you give a clear instruction, your children should know what is expected, and know what the consequences will be if they don't obey. They must also know when they are disciplined that it is because you love them, and you want them to bring them up well.
Discipline, in whatever method you choose, will be effective if you use it in that way. When you put your foot down, mean it. But don't be a crazed parent striking out whenever the mood strikes you, and calling it discipline!
Also, I don't think it's right to use an instrument to strike your child. If you use your hand only, only on their bum, you can strike to sting a little, but never to really hurt them!
As far as confusing your children about hitting others and being smacked - I was never confused about that, and my children are not either. They do not smack each other on the bum. When they hit, they are hitting in anger at faces, arms, legs, etc. Smacking on the bum for discipline is not done in anger.