I know no other way. And I had the posts lying around so seemed feasible.
The only thing is I’m going to do two of the shelves. And whilst I’m always a believer of you can never have too many strawberries. I’m tempted to put something else in the other shelf, but what???
Concreting? Next level 'llotment dedication. Only ever needed to use a steel digging bar to get posts in :)