One of my closest friends had a USP 9 compact that he wasn’t carrying. Turns out the holster he had were either uncomfortable or too obvious to observers.
Enter Sideguard holster and mag pouch. Problem solved. I borrowed that USP for a few days and, several time, had to check that the holster was actually in place. With a sturdy belt, the weight was that imperceptible. Concealment was also top-notch, with the gun and magazine invisible under just a tshirt.