Finally got my Aktenorder briefcase from Esde. Ronny was a pleasure to deal with during the whole process and would recommend his work if you're interested in any of his bags.
As previously said, it's made with thick shell cordovan with the reverse side as the exterior and with the straps with thick cowhide. Hardware is oxidized brass I think. Normally, he uses thick cowhide but I inquired if he can make one using horsehide. Luckily, he had shell cordovan.