The best markers I have ever used. They write smoothly without leaving gaps and it's rare for me to get one that doesn't write well. Their refills are expensive, but you can refill the used cartridge with ink from a bottle. Initially, I used the medium tip but after several hours of use and wear on the tip, they wrote quite thickly. Now I use fine, where after a few hours of use they write with the ideal line thickness for me. The fine ones also consume less ink.