You got it half right. Potassium chlorate and Na2 are both restrainers in that the shorten the scale (ie increase contrast) by making the highlights brighter. Much less effect on the midtones and shadows. The main difference is that Na2 works MUCH better in terms of print quality, but really works best with straight palladium prints. In general, the chlorate method gives sucky results, although it works with palladium and/or platinum. As Vaughn said, it's best to get the negative right to start with. But, with pure palladium and Na2 you can pull very nice prints from negs originally inteded for silver printing.