It have tested it with a normal 3x3 (as in the picture) and with a 4x4 and does its job without a problem.
Print Settings
It can be printed as it is.
Printed in PLA, without supports or rafts, at 0.2mm resolution and 15% infill.
Post-Printing
I would recommend putting some weight if you have heavy cubes just to give some more stability.
Also could be a good idea putting some adhesive clear rubber feet at the bottom.
The author marked this model as their own original creation.