I don't like diamond steels either, the diamond grit tends to tear the edges up on a good edge. A steel works by simply taking the microscopic edge you create on the edge of the knife and straightening it. And abrasive material actually serrates that edge and leads to a rough cut, and a much faster dulling of the blade.
This is just my opinion, but, even a smooth steel rod is better than most steels sold on the market nowadays. Diamond chips, ceramic, serrations etc...all gimmicks to get people to buy something because most people never understood why the old steels were just smooth steel bars