I first bought this pen a few years back out of curiosity, after being
recommended it by a friend. My pen of choice is usually a Steadtler refillable
technical pen (0.05), I have also used Tombow brush and Faber Castell Pitt pens
but I don’t like that they are disposable and they don’t have a huge amount
of line variation or give in the brush end.
I have recently revisted the Pentel's GFKP brush pen. It has a flexible brush
tip and can be refilled with specially made ink cartridges which are relatively
cheap and seem to last for ages. The pen gives a nice lush line with an easy
variability. The ink is dark and waterproof and can handle watercolour and ink
washes over the top. On some types of paper the ink can take slightly longer to
dry when heavily applied, but I have found this to be more about the paper than
the ink used in the GFKP. The pen is a great way to start practicing inking with
a brush before buying an expensive sable brush. You will probably end up liking
it so much you will not want to even pick up a sable brush at all.
If you have used the Pentel Aquash before, the GFKP pen is a lot more controlled
and better for finer more accurate inking. I still like the Pentel Aquash, but I
find them better for ink washes rather than detailed inking like the GFKP.