The reason the Remington factory extension was longer than the barrel, was so the end cap could be used as a bayonet mount.
Remington developed the extension as part of a military project, and the original extension clamp had a bayonet latch on the bottom, with the extended cap fitting the mounting ring of a bayonet.
Recently Remington has changed their barrel lengths on the 18" and 20" barrels to be 1/2" longer.
The new gun barrel length is now about even with a factory extension.
Aftermarket extensions will now be about 1/2" SHORTER than the new length barrels.
Vang claims his extension is better because it's machined from a solid steel bar, while others are made from steel tubing with brazed-on couplings.
In fact, how strong the extension is really isn't a factor.
The extension could be a piece of solid bar stock.
The determining factor is the GUN'S magazine tube.
The gun's magazine tube is relatively thin steel with deep, wide, square threads which weaken the thin steel even further.
Any bump or knock that might damage the extension will almost always knock the extension off the gun's magazine tube.
This usually damages the gun's magazine tube threads, which requires a trip back to the factory to have a new tube brazed in the receiver.
For this reason, NO MATTER HOW STRONG the extension is, you should use a barrel clamp to support the extension and help prevent damaging the gun from bumps and knocks.