I cannot get my head around the design. What possible application warrants one?

A traditional single wheel barrow is stable because it has a low centre of gravity. They retail at 50 quid with a fat, bump-flattening pneumatic tyre. The design is unchanged for a three-figure number of years for a reason.

Or you could pay a bit extra for a 4-wheel sack trolley. You can put a cow in some of them, still a fraction of the price of these things, and considerably more stable.