Hey, so the Kuretake Fude Brush Pen Extra Fine, which is also called the Fudegokochi (LS4-10S), seems like a solid pick if you're into detailed drawing or writing.

It's got this extra-fine tip that's a bit stiffer than a regular brush pen, which means you can have more control and precise lines — pretty handy if tons of detail are your thing.

But here's the catch: it's not waterproof. The manufacturer actually mentions that the ink is aqueous dye, so it'll bleed if it gets wet. That means if you're planning on using watercolors or mixing in other wet mediums, you might run into some issues.

From what we found, folks seem to like how this pen creates clean lines, making it awesome for detailed work or fancy handwriting.

The stiff nib helps with controlling line thickness too. Though, just a heads up, some have noticed that ink can gather at the tip, and a few felt it ran out faster than expected. Luckily, you can get refills for it.

Also, a few people have said there's some bleeding, especially on certain papers or when the pen mixes with wet supplies.

The manufacturer not being waterproof seems to fit with what they've experienced. There have also been occasional mentions of ink flow inconsistencies, and some got pens that seemed low on ink from the start.

In short, it’s a great pen if precision is what you’re after, but definitely think about whether these quirks might cause any issues for what you're planning to use it for.