This "square circle" is (I believe) just what I wanted for a "disappear-production" effect that I want for a routine I'm developing.
First, the "square circle" folds flat and and is carried into it's own flat carrying case. Second, the load area (which is a square) is very large. Third, the load area
has a bottom, so the interior square can be lifted off the base showing that "nothing" is there. Fourth, the bottom of the load box folds up for storage and for
a "reveal," if you want to use the box this way.
The only "complaint" I have is the decoration. The opening of the exterior box is i the shape of a spade from a deck of cards. I'm using the "square circle" for a gospel effect, so I'll have to do some "re-decorating" to turn the spade into a face of some sort.
I would highly recommend this square circle (which is really a "square-square (square) It has a very large load capacity. It is easily portable (no tube). It is very affordable.

Classic square circle mechanism. It is certainly easy to collapse and travel with. The load chamber is large. The only downside is that the folding sections don't lock into shape; you have to support the shape with your hand as you lift the sections; unless they are perfectly squared up it becomes challenging to replace the inner tube.
However, since it folds flat, you can unfold it in front of the spectators adding to the mystery of where it comes from.