It is designed to work in lieu with Markans resin model insert, his card holder and my card holder cap.
The small lip on the model prevents the resin models holder to fly around but stay put at the bottom. It is designed for a german box though. (28,7x28,7x7cm).
The model is shorter in every dimension than the box since the printbed of my MK3 is too small, but it works fine this way nonetheless and you have convenient finger cutouts to pull the cards out! ;)
The author hasn't provided the model origin yet.