Elegant simple design and thank you labsud for posting the OpenSCAD source! Let's all do that from now on :)
I printed the original model first using RealFilament Flex. The model is quite high, presumably to make space for the tenon and mortise. To save filament and reduce printing time, I reduced the height: mortise now shows through two holes on each side, but I found it works just fine even so. Requires a very small amount of easy to remove support.
Also reduced hole diameter by 0.05, because my rusty old bit collection (now nicely organized) appears to have minor size variations, causing some bits to fall out if upside-down. Narrow bits can now go all the way down to stick, but I push wider ones in just a little to make them easy to remove. Works great! If I need more bit storage in the future, I'll try to modify this model with round, ribbed holes, which might just do the trick with a flexible material.
Real Filament Flex