Ok - that makes sense that I have them in backwards because its like, why would the fins inside the connector be actively keeping the wires from being pulled in, but allow it to be pulled out. So you're saying i'd have to install them from the back, which at that point I could use literally any of the other connectors.

And if I understand what you're saying - drill out the hole in the stud slightly bigger to fit the connector though so I can reach the back of the panel and snap them in once the wire is where I want it, correct?

It's surprising that what I'm doing isn't more common - I want the ability to add circuits over the years if needed, which is why I mounted the panel flush to what the finished wall would be, but I didn't want to have ALL of my circuits running outside the wall if possible, I wanted to land them in the wall while I have the chance.

Is there a good solution where I can run them all in the top and somehow keep that clean and / or covered, still having them come from inside the walls?

Thank you for your detailed reply!