I've been looking at some Remington 870 plus two magazine extensions and I've seen an assortment where it seems clamps are suggested and some are not. The Vang Comp types seem to suggest no clamp while the Nordic Components seem to specify clamps. It's not just these specific brands, but seems split across others. What is the forums experience with shotgun barrel/ magazine tube clamps?

Of the two I've used both have used clamps. In both cases the clamps were also the sling QD fitting. IMNSHO the clamp adds some rigidity and makes it harder to miss align the extention in the case of rough handling.

For a +2 extension, I usually don’t bother with the clamp. For my semi-autos, you usually have to remove the end cap or extension to remove the barrel for takedown/cleaning, and it’s just a little more hassle to constantly remove/install the clamp.

I have two with, one without. One of them with would be fine without.
No need for it on a +2 with a quality tube.

I have seen guys running a +8 longer than the barrel with no clamp.

I myself use a clamp on my Benelli for 12+1. With a +2 I wouldn't bother.

I’ve been very pleased with S&J Hardware extensions, not the cheapest, but this is one of those buy once, cry once items. No clamp needed but the magpul clamp/sling mount works great in combo if it makes you feel better.

Depends more on how beefy the extension is. When I used an 870 with a +2 I settled on the gg&g. Thing was a tank. No clamp needed. Prior to that I had the remington factory one and it needed it in my eyes.

I use a +1 nordic on a sbs benelli now so no clamp needed. See how the tube is first and go from there. As its been mentioned though, the clamps offer a nice spot to mount the sling as well. So maybe useful just as that alone.

I installed one to limit the chance of something getting snagged between the barrel and the magazine.
More beef doesn't hurt, especially if somebody grabs the front of the barrel in a fight.

I use the scattergun tech extension as it comes from the box, no clamp. I'd follow the manufacturer's instructions on whether or not to clamp it.

I had a buddy who had chucked his shotgun in a barrel hard enough to break his extension at the threaded area, but was still able to finish the match because the clamp was holding it all together.