I had some trouble with the original plug design, if you're not careful you can push the plug too far in and then you need to get a tool to try and depress the disconnector ring on the bowden fitting.

This is meant to remedy that by giving you a 5mm window almost all the way around. So that you can more easily depress the disconnect ring with a (small) finger, fingernail, or almost any screwdriver. 

Recommend printing with more infill than you might normally, I went up to 60%. It doesn't add significantly more printing time and strengthens the thin 4mm stem.