Even without a tire over them, they weigh more than the heaviest tire on the market. So, yeah. Exactly.

It lighter than a tube on a dirtbike. It makes the rotating mass less.

On a mountain bike the amount of material you'd need would definitely be a little bit of added weight vs tubeless. But it probably wouldn't be a whole lot more substantial than tires full of sealant. Certainly wouldn't be any more than these doubledown sidewall tires, which would be substantially heavier. The only way they fail is if the tire fully comes off the bead. We use rim locks on dirtbikes to prevent that, but dirtbikes also weight 250 pounds, and they produce a lot of power under throttle. You wouldn't need that with a mountain bike tire.

It would beat flat tires trailside, having to constantly reinflate a tire that's been sitting, and it would eliminate the mess of sealant.

So faster, heavier, more powerful, but the comparison isnt useful?

Just so we are clear, I don't have any air in my tire. No tubes, no messy sealant, no tubeless. It's a foam core. It can't go flat, and you get traction for days. It's not cush core, or any of the alternatives, which is where I think they went wrong, because those all still require air. Air is one of the biggest, if not the biggest failure on a mountain bike. They don't weight all that much either, I'd take an extra few ounces of rotating weight vs futzing with air trailside.

Yep. I use inserts on my on road car rc racing car too.

It'll get squeezed and/or flung out the next revolution of the wheel though