A few other things that can help:

- for the “it can work itself out” problem, I’ve had pretty good luck on other projects by making a standardized “dual dovetail” (bowtie) male/female slot with clearance tuned so that the male piece fits tight into the slot. Printing the male part flat on the bed means that the filament is oriented correctly for strength

- integrated zip tie slots. One design I worked on that was similar to what OP did but needed better grip… I made the slot where the folded over timing belt meshes longer, removed the printed centre pin, and put two integrated zip-tie slots: one near where the centre pin was, so I can use the zip-tie ratchet to actually pull the belt backwards and put tension on it; the other was near the mouth of the jaws, so that after tensioning it I could use a second zip-tie to “lock” the jaws onto the belt

- a third one: you make a little block with dovetails that looks like the “circle plus mouth” piece from this post, but also include a pocket for a nylok that you can use to add tension to the belt after getting the belt secured inside the clamp.

I have tried printing teeth that would mesh with the belt but didn’t get particularly good results from that. Possible that newer printers have better resolution and could print the teeth better, but my test with that just ended up with a little bit of a rougher surface and the teeth couldn’t actually mesh.

Conversely, with this design the center pin could break loose and the belt would still hold, because the pin just has to stop the loop from fitting through the slot.