In my opinion, some are similar to deco scissors - like the simple scallops ones, but MUCH easier to use. You can easily make a straight edge with the punches, but it is hard to do with the scissors and they don't line up well.
Others are not like deco scissors at all, they are more like an elaborate die cut- like these.
I use my deco scissors all the time. They are really nice when you want a simple, elegant border. I love my edge punches too, but sometimes they're just too much for what you need. If you draw a straight line on the reverse side of your paper and use that as a guide, you can get a straight cut. I use mostly Fiskars deco scissor since they are about the best quality ones I can find around here. I usually end up giving my niece the ones I don't use, but I have about 15 or 20 deco scissors that I use all the time.