I purchased the POSCA in an attempt to find my holy grail- a white brush pen.
Unfortunately, the POSCA has a lot of issues that prevent it from being such.
1. The ink is watery, and will reactivate non-water-safe ink if applied on top
(very important if you're a comic artist, and are using the white brushpen to
make corrections) 2. The ink isn't fully opaque, so even if it does not
reactivate the ink beneath it, there will be some ghosting 3. The pen is
pressurized, and may leak during barometric pressure shifts (or in an airplane
cabin). Unfortunately, I do not reccommend this product.
I'm a comic artist, and I've been using this brushpen in lieu of an actual brush
for months. Very convenient to carry around in my inking pouch, and it fits the
hand better than other brushpens I've purchased in the past. The brush has a
great amount of give, allowing for some really expressive lines, and the
brushpen is fantastic for both serious inking and noodling about in a
sketchbook. My only complaint is that I can't refill the cartridges with my
choice of ink, I've found that any ink besides the ink in the Akashiya
cartridges clogs the natural bristles of the brush. This is a problem as the
Akashiya ink is slightly greyer than the other inks I use, and requires a little
extra tweaking in Photoshop. Other than that, a great product.