I'm firmly in the "cold bending" camp. I worked for Sig and can tell you first-hand that they have been bending all their wire cold for over forty years.

I also love K&S wire benders and use them often. However, the coil bender has a design flaw IMHO. The handle has a grooved post that engages the wire, but it is too tall. When you come around with the wire, the post will bump into the very wire you are trying to bend and results in gaps between the coils. Normally, you want the coils side-by-side with no gaps. I modified my bender by simply grinding down the height of that grooved post so that it won't interfere with the coils as you are bending.