The stick on/velcro side saddles are great as they work similar to a plastic one, but are removable because of the velcro.
This works great in combination with chest rigs or pouches that utilize velcro. You can pull a full one off your vest, and replace the empty one on the shotgun.
For example when used in with the S&J shotgun pouch or the Blue Force Gear LMAC (with bottom MOLLE flap removed).
The S&J stick on holder also won't leave any residue when you decide to peel everything off.