I have a conversion barrel for my G20SF. Who doesn't like the option to shoot something different w/ a simple barrel swap? I don't use the 357 Sig barrel for self defense. It's strictly for range fun. And in that role it's great. Lots of flash and noise
I have little doubt it makes a great SD round. I have to many other options. Shooting the 357 Sig costs more money than other options and is one of the reasons it's hasn't grown in popularity. There are police departments that use it so it's not a complete oddball.