IIRC these were in fact
BikeHods Waitrose used to flog you the bike hitch for a deposit which enabled you to used the trailer,taking your shopping home and then bring it back with the recycling.
The early bracket was simplicity itself, a U bracket with a stub that attached to the seatpost, the trailer had a piece of rubber hose attached with a jubilee clip. This hose then slides on to the stub and is held in place with a pin. Later versions used Weber type coupling
In many ways the forerunner of the Burley Travois design.
I remember seeing the inventor arriving at one bike conference with half a dozen linked to each other like a train
We have had one for many years with the Carradice bag
It is a good trailer with the advantage of being able to push around as a shopping trolley, then fitting easily on to the bike in seconds
On the road they need careful packing as the pivot / bracket is high they have to be packed with heavy stuff at the bottom or they lose stability. Even then if it overturns, it is not unrecoverable and will not have you off of the bike.
Try one and decide for yourself!