The Golden Rule of upgrades is don't put ****ty parts on your gun. You wouldn't intentionally do that, would you?
A well-made extension from a good company does not a require a clamp to hold it in place so don't buy a crappy one in the first place. The Remington extension works but it is overly complicated and contains too many parts.
Buy your extension from someone good like Vang, Scattergun, Nordic or S&J Hardware and call it a day. I use the Vang on my 870P and am very pleased with it. It's a "Set it and forget it" kind of part.
"Of every 100 men that go to battle 70 should not even be there, 20 are nothing but targets, 9 are true soldiers, and we are lucky to have them for they the battle make but ONE, one is a warrior, and HE will bring the others home." Hericlitus