I first became interested in the SIG P320 because of its much touted (by SIG) modularity. I seldom carry but I saw in the P320 the option of having a full-size pistol chambered in either .40 or .45 cal and a compact 9 mm by buying a 9 mm compact caliber X-change kit. I had no prior allegiance to SIG Sauer, had never owned one, and always considered them rather overpriced.
Early this year I had the opportunity to shoot both the full-size P320 in .40 cal S&W, and an HK VP9, both as rentals at a nearby range. I preferred the P320 as it seemed to fit my hand better and I shot it better, despite not being a huge fan of .40 cal. The VP9 also had a tendency to pinch my trigger finger against the bottom of the trigger guard. I decided to wait for the .45 cal P320 which SIG had already been promising for around 6 months or so. I have shot Glocks but never been a fan of them. They don't feel good in my hand, and the stock triggers on the P320 and HK VP9 were much better than those on any Glock I have shot.
Last April Fool's Day SIG raised the price of the caliber X-change kits by $100 overnight without advance warning. They are now priced at a point at which buying an X-change kit instead of a complete new pistol makes little sense for the vast majority of people. What is more, when SIG finally released the .45 caliber P320 this fall, we found that the FCU for the .45 will not work with the other calibers so the .45 ACP is a stand-alone platform. But SIG did not have the grace to announce this publicly, they just left it for people to figure it out on their own, one by one. The incompatibility issue of the .45 caliber with the other calibers is not a big deal for me since the X-change kits are priced so high I would choose to just buy a complete second pistol. But it was a disappointment for some.
Needless to say, I think SIG has screwed the pooch big time with the roll out of this pistol which has probably not helped its popularity. Nonetheless, I believe it is a good pistol and did, in fact, buy a full size .45 caliber P320 which I got with night sights NIB for just under $500 out the door. I have only shot a couple hundred rounds through it so far but have been very pleased with its performance. No malfunctions (with FMJ ammo), good recoil absorption, good accuracy and a very nice trigger. The medium grip module on the full size feels as if it was molded for my hand.
I also shot a HK VP40 and thought that was a very nice pistol. The HK VPs have a bit more take up in their triggers and the P320 trigger just seems to work better for me. Others feel the opposite. I have not yet had the opportunity to shoot a Walther PPQ.
I may buy a compact 9 mm P320 for carry. Actually, I would probably buy the "carry" model P320 with the compact slide and full length grip module for range use, and buy a compact grip module and a couple of the shorter magazines for the compact. A grip module and a couple of mags can be found for not much over $100 if you shop around. So to this extent the "modularity" of the P320 still holds water for me. But my frustrations with SIG's business practices will cause me to very carefully examine some other alternatives first.