Well take what I said with a grain of salt. I have never used such a knife myself. I have only seen it used (in a test of knives with cullens) on Americas Test Kitchen. They tested a number of knives with cullens that did not do anything at all, but one with cullens on the entire surface and on TV at least, it worked as advertised.
I would not buy a knife because it has cullens. Well not now at least. I did buy one with cullens before I knew better. The knife itself is fine, but the cullens do nothing. If I were buying a knife I would not choose one because it has cullens. I would also not dismiss one because it had them. If I had a choice of the same knife with or without then I would get the one without unless it had them on the entire surface in which case I would consider getting it with.