I was really enamored with the round about 15 years ago. Once I realized it really wasnt really all that different than some 9mm, and the price skyrocketed, I went back to 9mm. I havent regretted doing so either.
I had six guns in the caliber, five SIG's (226's, 229's, and a 239) and a Glock 31. The 31 was the one that clinched the deal for 9mm.
The 31 let me shoot it against a comparable gun, the 17, and I came to realize, there really want any noticeable difference shooting them, between 357SIG and hotter 9mm, +P, +P+, or even standard loads of 9mm. The "bark" of the 357SIG, and the beating the 31 was taking from it, were the only things I did notice. Never had the battering issues with the SIG's either. Nor did I with the 17's shooting a steady diet of +P+, which is basically the same PSI as 357SIG.
Other than wanting to try something different, which is fine of course, I just dont really see any pluses to it now. Factory ammo is now more expensive and reloading for it really isnt cheap either. At the time I was shooting it a lot, it was still the same price as .40S&W when you bought it in bulk, and only cost me $1 more a box of 50 to buy factory, than to reload it, so it really wasnt worth the bother.
Once Obama got in, and that ammo shortage took off, all that changed. Factory ammo went up to as high as $600/1000 (I was paying $250). I about doubled my money selling off the unopened cases of 357SIG I had too.
Reloading became more economical then, but 357SIG still costs more to reload (or at least it did then, and Im betting it still is) than 9mm, as bullets really are not interchangeable, you need caliber specific bullets for the 357SIG, and you use more powder.
I dont think there anything wrong with the round, I just dont see, and especially for the money, that its doing anything 9mm cant do. I can also practice a lot more with 9mm too, because of the difference in cost.
Since youre getting free ammo, the easiest way to find out, if you have a .40 caliber gun, is get a factory barrel in 357SIG, and some mags (you may or may not need them too), and try it out. Most youll be out, is about $150, $200 or so if it doesnt work out.