Dressing sets are usually junk. They are considerably cheaper, and there is a reason for that. I tried to used a dressing set on one ocassion, the thread I was trying to fix was harder than the metal in the dressing set - basically destroying the die.
If you are worried about price, and you don't use them very often, just buy the tap or die that you need. They are avaialble separately.
Don't buy a tool that is insufficient to do the job.
