.357 SIG is a pretty cool cartridge, but really it's time of obsolescence is arriving. It was never really a popular cartridge and not many departments/agencies adopted it. It seems like the Secret Service, the Delaware State Police, US Air Marshals, Bureau of Industry and Security, Texas Department of Public Safety, Virginia State Police, and Montana Highway Patrol were the only agencies/departments who issued it as their primary service pistol cartridge for any real length of time, and there are a few others who have adopted it more recently, but compared to .40 S&W, 9mm, and .45 ACP, it is a pretty rare duck and I don't think it's going to stick around long considering modern +P+ 9mm ammo performs just as well with lighter recoil, higher capacity, wider bullet options, and better availability.
Hell, more and more departments/agencies are even dropping .40 S&W and going back to 9mm because newer bullet designs have improved it's effectiveness well above what it was in the 80s and 90s, and with lower recoil and higher capacity. Even the FBI is moving away from .40 S&W and going back to 9mm, and they were the ones responsible for the creation of .40 S&W (because their city slicker agents were too pussified to handle 10mm Auto when they adopted the cartridge in the early 90s). Their new contract for duty sidearms with GLOCK is for GLOCK 17Ms and 19Ms, though special agents will likely still be allowed to buy, qualify, and carry GLOCK 21s, 22s, and 23s if the agent prefers to carry those calibers, and the subcompact GLOCKs in the same caliber as their primary sidearm as backups like they have been for years.
It is kind of a shame that .357 SIG didn't get more recognition and popularity. It's goal to offer similar performance as a 124gr .357 Magnum with higher capacity, lower recoil, and faster reloads than a wheelgun was admirable, but then a lot of cartridges/weapons fail to live up to the potential we may see in them. My beloved 10mm Auto is finally gaining the following I always felt it should have, and more and more ammunition companies are loading it to it's full potential instead of basically making it an overly-long .40 Short and Wimpy. Because for the longest time anyone who made 10mm was loading it to the asinine FBI Special Light Load specs, which is what the original loading specs for .40 S&W were based on. The .41 Magnum always deserved more love I've always felt, but aside from a similar situation as .357 SIG where a handful of departments adopted S&W Model 57s and 58s (usually for highway patrolmen and motorcycle troopers), most departments were happy with .357 Magnum and most sportsmen figured .44 Magnum was superior because it was "bigger" despite it only being marginally more "powerful".
.357 SIG kind of found itself in the same rut as .41 Magnum where departments/agencies had a hard time seeing the point of adopting it when there were several other perfectly serviceable cartridges on the market. Why have the same capacity as a .40 S&W with a smaller, lighter bullet? Why have the same bullet diameter as a 9mm and carry less ammo? Plus it tended to be more expensive than 9mm and .40 S&W, fewer ammunition manufacturers offered it, and fewer gun manufacturers chambered their firearms for it compared to the Big Three (9mm, .40, and .45).
But I'll never tell anyone that they're wrong for owning or buying whatever weapon or caliber they want. I totally get feeling the "fizz" over a certain weapon or cartridge. I absolutely love my Smith and Wesson 57 and the .41 Magnum it's chambered for. Would I be just as well serviced with a S&W 29 in .44 Mag or Model 27, 28, or 686 in .357 Mag? Probably. I love those guns and cartridges too. But I really love that the .41 Mag bridges the gap between those two cartridges and is an excellent balance of their performance. Nearly the same muzzle energy as .44 Mag, but flatter shooting and felt recoil is closer to .357 Mag. The 7.5fk gives me the same fizzy feelings and I've wanted an FK BRNO ever since the Field Pistol hit the market. I just don't have $7500 to drop on one. But I'll definitely be doing what I can to get the PSD since $1650 is doable for me, and it has the benefit of being able to also chamber more affordable ammo that's more widely available. I'll likely get it with the 10mm/.40 S&W barrel for the second barrel since I don't own a 10mm Auto at this moment, but I'll likely also get the 9mm barrel, recoil spring, and magazines to be able to take full advantage of the PSD being a multi-caliber firearm. Firearms that can swap calibers have always had found a soft spot with me. I just think it's awesome that you can have one gun that can utilize a wider variety of ammunition. It allows you to use the cheaper stuff for practice and training, and save the expensive stuff for when you might need it to end a problem. Of course, if you carry a gun you should always practice with the ammunition you plan on having in it when you carry so you know how it'll act if you actually have to use it, but it's like when .357 Magnum was the most widely used sidearm cartridge with law enforcement. Officers would practice mostly with .38 Specials loaded in their sidearms, then switch to .357 Mag to qualify and when they were on duty.
Edit: tl;dr: Bottlenecked cartridges are awesome, some weapons/cartridges don't get the love they maybe should, sometimes cartridges become obsolete because new technology or manufacturing makes older cartridges perform at the same or similar level, buy what you like and be happy because fuck what anyone else thinks.
