I must admit, when testing this pen, I was recovering from a migraine, so my memory of the pen's performance is a little hazy, especially since the pen doesn't particularly stand out in any positive or negative way.
As a heads up, the ink in these pens is waterbased and a combination of dye and pigment. These pens are not suitable for inking something you intend to watercolor over, as it will reactivate the ink, but you may be able to do a neat quick inkwash effect. I'll have to write back to you guys with the results on that one.
I believe this is the older style of packaging- it seems like most Japanese pen companies have moved from the plastic and cardboard package to a thin plastic bag with the pertinent information printed directly on the plastic.
Plenty of companies make pens that work the same way this pen works- the body of the pen is soft and contains the ink, there's a divider that keeps the nib and the ink cartridge separate during shipping, and you remove the divider to activate the pen. The Pilot Brush Pen fine reminded me a bit of Pentel's brush pens, except the brush nib is much smaller. The back of the package explains how to assemble the pen.
Right now the brush is all clean, as the ink hasn't had a chance to flow into it yet. That'll soon change.
The white plastic ring is the divider that keeps the ink cartridge and the brush separated. To remove, you unscrew the two halves, remove the plastic ring, and pop the brush nib onto the cartridge.
It took a couple minutes to get the ink flowing into the brush. I like to expedite this process by propping the pen brush side down, to increase ink flow.
The black ink in the Pilot Brush is very black and highly pigmented, much like the Pilot Pocketbrush Soft. I really like this rich, dark ink, and I'll have to do further testing to see how water/Copic/erasure proof it is.
The Field Test
So this nylon bristled brush pen handled like...a nylon bristled brush pen, albeit a finer tipped one with a nice rich ink. This pen lays down ink quickly, unlike the somewhat stingy Pentel Pocket Brush, and is capable of both fairly fine lines and nice thick bouncy lines, all without the risk of your pen going mushy. I don't usually use this type of brush pen- I've had a history of them leaking in the past (especially when flying, yikes!), but I really like the Pilot Brush Pen Fine.
In general, I think I've mentioned that I'm not the biggest fan of nylon bristled brush pens, due to a variety of issues ranging from 'gray ink' to 'tendency to drybrush' to 'hard for me to handle'. Of the nylon bristled brush pens I've used and tested, however, I like the Pilot Brush Pen in Fine a lot. It's refillable, both with cartridges you can buy on Jetpens, and probably also with a steady hand and a syringe full of the black ink of your choice.