What's the difference between a hog-ring anvil and a friction-ring anvil?

A friction (detent) ring holds the socket with a spring detent and lets you swap sockets quickly by hand; a hog-ring (retaining pin) anvil locks the socket more securely, which reviewers prefer for heavy truck and equipment work where sockets take abuse. DeWalt's high-torque models in this pool use a hog-ring anvil, while the Milwaukee M18 Fuel listed here uses a friction ring.