Cool find! I have a note-taking system that uses bullets, but isn’t exactly bullet journal. It doesn’t deal with the indexing—probably closer to this system. Although, I did just move to putting it in a text file instead of keeping it in a notebook.
The today, next and someday concept that are interesting. I’ve found that those things that are due farther in the future tend to not be well-defined and don’t necessarily make sense as tasks. Others may see it differently.
Ugmonk sells solid gear. I’m certain cards and the holder are quality.