However, I do notice flow problems when I use standard international ink cartridges from other brands.

My higher end fountain pens don't have this ink flow problem...

But I learned how to take care of the pen by cleaning the nibs every time I changed ink colors, and the ink flow problem was solved

And when I switch to using an ink cartridge that didn't come with the set, ink flow problem became constant.

It is supposed to come with the following nibs: Extra Fine (XF), Fine (F), Medium (M), Broad (B), Extra Broad (XB).My kit has the following, XF, F, M, B,