This fingerboard is designed to be able to train both hands with just one device. You can easily adjust the intensity by positioning the device more on the fingertips or further back at the joints.
The unlevel surface makes it so every finger is in a proper half/full crimp position.
Print with at least 4 walls and somewhat stable infill. I higly recommend using fuzzy skin to make the surface a little bit more grippy. According settings are already adjusted in the .3mf file for Prusaslicer.
Thread some straps/paracord/fabric through the slots on the side. Whatever you use should go around the back, this way we do not only rely on the strength of the 3D-Printing material to keep the device from failing. For reference see the picture below.

The author marked this model as their own original creation.