I used Seitz-Kreuznach Arctic Blue in cartridge form, in a Kaweco Sport with a 1.1 mm calligraphy nib and also with a fine nib.
This ink is lovely, lighter shade of blue or turquoise with nice shading. It dried quickly and cleaned up very easily for me. I noticed that occasionally Arctic Blue hesitated on startup, but when that happened ink flow was fine after a scribble or two. And that might have been a function of the cartridge or of the nib and feed, rather than the ink itself. Arctic Blue was notably resistant to feathering even on my worst paper.
To get a better idea of the color, here is a closeup of Arctic Blue with the darker Diamine Turquoise above and the standard blue Parker Quink Blue below.
In hue, Seitz-Kreuznach Arctic Blue fits right in with Pelikan 4001 Turquoise and Caran d’Ache Hypnotic Turquoise.
Arctic Blue has almost no water resistance, which is the flip side of its easy cleanup.
Paper towel chromatography of Arctic Blue is below.
Seitz-Kreuznach sells Arctic Blue at a great price, with very reasonable shipping charges. Living outside the EU, I order from Seitz Global, which offers Seitz-Kreuznach ink in 100 ml glass bottles for $9.90 and in 20 ml glass bottles for $3.25. Short international cartridges are $2.19 for eight or $3.62 for 14. George Seitz kindly added this cartridge to an order I placed, so I could sample the ink, before they started selling the smaller bottles.