Here's a little assortment of pictures of how I'm using mine for bullet journaling. :)
The pages of the "official" Midori inserts seem like they'd be too thin for watercolor, but I have to say -- I was pleasantly surprised. As long as you don't do a lot of scrubbing, both pan watercolors and peerless colors seem to have almost no bleed-through. Also, Tombow dual brush markers "smooshed around" (the scientific term...ahem) with a waterbrush are almost perfect, too, with only a little bleed-through when I got a little heavy handed with the scrubbing.
I LOVE my Traveler's Notebook!
Project Made In: Traveler's Notebook Basics