I picked up the St Action Pro 12GA Gauge Shotgun Safety Trainer Cartridge Dummy Shell Rounds with Brass Case, Orange, 10 Pack from Ultimate Arms Gear as a training tool, and after putting them through their paces, I can give you the straight assessment. These dummy shells fall into the firearm training category and cost me $13.94, which is reasonable for what you get. Having spent years in the Marine Corps working with shotguns in various conditions, I know the difference between quality training equipment and cheap knockoffs. These are legitimately useful.
The St Action Pro 12GA Gauge Shotgun Safety Trainer Cartridge Dummy Shell