I was pondering that while drawing it actually. There's a tiny little nub which is supposed to hold it in to the handle, but given how loose it is, the nub obviously isn't enough. Its much more square on my printed version so that already holds it in better, but there is plenty of scope to make it larger and I'm also tweaking the design so the whole clip is a tighter fit in the handle. All of that should make them considerably less likely to fall out, and the choice of colour was quite deliberate
Replicating the door card clips with this type of technology is practically impossible (at the moment) due to the level of detail and the strength required for them to snap together. My thoughts on that are to actually redesign it using a flexible polyurethane 'grommet' in the door itself (reusable hopefully) and possibly the original pin on the door card. That will need quite a few design and test cycles, and I need to print a new printer which can handle polyurethane (since the CR-10S doesn't). Since I have 200+ door card clips in stock, that one is going to come along later
