DRC - once you pop the original refill seal out of an OEM BCI-6 cart, the computer friends blue plugs are as convenient as a pop up top. There is an easily gripped tab to pull it out, and it is large enough to handle and replace after refilling. I used them for my first efforts at refilling as I was using the original OEM carts that came with my printer. When I started using other carts as well for backup it became more convenient to have a uniform system and the s.s. screw/o-ring worked out really well. You are right - a popup fill hole cover would be great.