Can confirm, MUJI notebooks are of a decent quality and they can handle fountain pens as well.
In addition to that, I gradually switched to their 0.38 pens of different colors. With fountain pen it was more stylish but impractical for multiple semantic(*) colours. With cheap, light, yet nice quality pens of different colours I can not only carry multiple ones, but have the same set at multiple places.
(Dark blue is body text/drawing, light blue is comment/secondary annotation, orange is action/process/message passing, green is data/metadata flow, …)
In addition to that, I gradually switched to their 0.38 pens of different colors. With fountain pen it was more stylish but impractical for multiple semantic(*) colours. With cheap, light, yet nice quality pens of different colours I can not only carry multiple ones, but have the same set at multiple places.
(Dark blue is body text/drawing, light blue is comment/secondary annotation, orange is action/process/message passing, green is data/metadata flow, …)