Yes these sound great but Sep Holzer made them to use up a surplus of tree trunks he was clearing on his alpine farm. For most of us, tree trunks are scarce! or valuable for burning.
In 1981 I made a mound rather than hugelbed, with twigs as bottom layer then leaves, grass and soil/compost on top. This gave good harvests for three years, same principle of slow breakdown and more practical for most of us. Moisture retention was good – but no better I felt than where using a good layer of compost.