From what I know they seem to work. They aren't as accurate as a fully rifled barrel, but better for most people than a smoothbore. My hunting buddy from childhood used to make these in his machine shop for one of the companies that market them. He used a process where he pumped a saline solution through the tube that had a sleeve with rifling on it. The rifling was cut when the electricity and the solution was passed through the tube. He said the Russians used to use this method to rifle cannon barrels. It is sort of like a EDM process and seemed to work well. I still have 1 or 2 he made and gave to me. I use a rifled barrel so I haven't tried these in many years.
