Thanks for your feedback! I liked the idea of measuring the strength of the slide connectors so I have created the following video for you: https://youtu.be/r5TO2mwobMY
When designing the bricks, I experimented a lot with different types of slide connectors, e.g. prismatic vs. cylindric, solid vs. concave, thick vs. thin. Even if it is not the strongest one, the current type turned out to have a number of advantages compared to others: (1) Because it is concave, it can be pulled out using a needle-nosed pliers, (2) it leaves space to hide cables when using the bricks in combination with electronic devices, (3) it provides some elasticity, (4) it provides a predetermined breaking point so the other parts of the model will stay intact when the model breaks.
If the connectors should be too weak for certain applications, one could still experiment with different materials (in the video I am using PLA with a 0.15mm layer height), print them vertically rather that horizontally, or make the connectors slightly thicker by adjusting the corresponding parameter in the OpenSCAD source (see http://kbricks.org). Also, chains of multiple cubes could be provided out of the box.