The 357 Sig is a very good round and the 357 Sig is pretty comparable to much of what is sold as 357 magnum ammo, especially in short barrels and light bullets. In fact, Winchester loads the 357 Sig slightly hotter than the 357 magnum in their PDX1. That said, the 357 Sig can't keep up with real 357 magnum loads, especially with heavier bullets. In a pistol, the Sig is the more practical cartridge but it won't replace what the magnum will do in a large handgun.
Btw, my EDC is a 357 Sig and I also have a 6" GP100. I like both and they each have advantages.