They have a nasty habit of destroying themselves, but if they can get it to work it's a fame changer, no nasty explosives to carry around and a shell that goes Mach 5 is impossible to defend against with current technology. It's a very very big if though.....
Think the Zumwalt is a bit different, it uses fancy hybrid shell/missile technology which is why the rounds cost $800k each, and since they're not building many more ships the supply of said rounds has dried up.