Re: Really interesting choice. The Sig 320 is unique in that the only part of it that is serialized is the trigger group, hence you can get a kit that changes a full-frame to a compact to a sub-compact, 9mm to .357 Sig to whatever
That is a great feature if one lives in a country like Germany where it is difficult to get a pistol permit. One gun does everything. However, this is the USA where it is relatively easy to get a gun if one is not deranged or a felon. Never met a single person who used this ‘feature”.
My brother does. He competes with the full-frame version with the 5" barrel and optics, and he carries the compact version with the 4" barrel. Former in 9mm, latter in .357 Sig. A new frame and barrel kit costs less than a new Sig. YMMV. But you are correct that licensing is an issue because he lives in one of Those States.