Got a reply from Aevon themselves, badly google translated as follows:

Hello,

>>>> it did not seem very prepared and I'm afraid that it messes up the seat post.
On the contrary, the coupling ball is composed of a nylon high density which allows the trailer "horizontally pivotable" up to almost 180 ° around the seat post.
It is therefore possible to make a U-turn on road without setting foot on the floor.

The same ball can also rotate vertically: this is essential for MTB use.
It was designed to withstand mountain bike use with 35kg load.

Finally, choose the diameter of the coupling according to the diameter of the seat tube of your bike.

Sincerely,

Frank Team Cycloboost