I just saw this video, and this tube idea looks pretty cool, saves the need for taking off the frame when fixing a flat!
Has anybody tried a tube like this before? particularly in trials/street riding, im wondering whether it works well 
thanks.
EDIT:
picture of how it goes together
does the air go all the way around or is there a small break? it could be an issue, although i dont see how.
I think there’s a small break, but the two ends overlap each other so they come together with no real break at all
Looks like something that would be extremely useful for racing! Not so much for casual riding, where you’d have to bring the spare tube with you for it to be useful. But for people on long tours, or anyone who carries a lot of junk with them anyway, they might love it as well. It could replace several other tools (depending on the design of your uni) so it might be only a space penalty and not so much a weight penalty. I expect they are quite a bit pricier than regular tubes also…
As far as i can see they retail for $9.99
The cheapest 20" tube i’ve found over here was £1.99 which is about $5 I guess.
They are pretty expensive then 
I expect they don’t make them large enough for a 36" tire, maybe they have a size that two of them would fit, with an extra valve hole drilled in the rim.
May provide a lighter 36" tube without over stretching a 27" tube…
followed up on the 36" wheel tube idea I had posted.
I only found 20" wheel cobra tubes offered, 62 inches long. A 36" wheel is about 112" So two 20" wheel tubes would probably be too long, by 12 inches.
Interesting idea, but…
It probably creates a lump or a low spot at the joint, so it probably isn’t very good for normal riding. Even if it looks round when just sitting there, I’d expect the joined area to not compress as well, so it would be like hitting a little bump every revolution. If I remember correctly, at anything over slow speeds, the slow down from bumps is second only to wind resistance for slowing a rider down. (Especially for me on my muni…) Absorbing bumps is the purpose of pneumatic tires, so I’m not interested in anything that compromises that.
Now for trials riders… Since they don’t do that much rolling and are probably more prone to pinch flats, it could have some benefit. You’d have to build your wheel so that the valve stem isn’t in one of your favored landing areas if you wanted it to perform as well as a normal tube. Easily fixing pinch flats would be the main benefit, since it isn’t too hard to fix other flats without removing the tube. But I think you’d probably be better going tubeless…
Actually this would be almost ideal. You would have about 3" of overlap at both ends. The tire defines the space, and the tube simply holds the air. Where there is overlap the tubes would make space for each other as they are confined by the tire. There wouldn’t be any bumps or flat spots due to the tube. If you get a flat you would only have to replace one of the tubes. Still a bit pricey, but a good idea.
EDIT:
I wrote that without looking at the photo again, and forgot that the tube joins at the valve. I’ve seen tubes like this in the past that had the valve in the middle, and that would be more like it for a coker.
That’s no big deal, if you’re using 2 20" tubes. You just drill a second valve hole half way around and join them at each valve.
That looks pretty cool, it could be good if you get a flat in a comp, it would be way faster to change your tube!
i ride bmx and iv rode those tubes they are really good
I think you would want that overlap so that the tubes can equalize each-others pressure. Sort of like how a Zodiac boat has a big pocket at the intersections of its tubes to keep the pressure the same on all sides.
Interesting “OLD” idea
Yep,
Been there done that, years back we had a similar tube for racing so the wheel stayed on the bike called “The Dirtworm” and I believe it was marketed by Specialized. Those would overlap and inflate with no gap, a no tool tube change!
they look easy to make from a larger tube. its really not a bad deal at all.
…Which begs the question: Why isn’t Specialized, or someone else, still selling them? Maybe it’s too “specialized” an item? Any innertube sold in a box (retail) is most likely going to be used as a replacement, so why not one that’s easier to replace? I wonder what we’re missing here…
Or maybe other versions did indeed have a lump or soft spot at the join, so they were never popular. Also there’s an uneven spread of mass around the wheel, which might be felt by the rider. Probably more on a bike than on a unicycle though, except for people doing balency tricks like coasting, gliding, etc.