It is a very strong habit pen. ものすごく癖の強いペンです。
This is a brush that does not blend with border of watercolor.
I can use it from line drawings to painting, but I think that it is not suitable for everyday use (because it is hard to become painted as expected)
Conversely, it is recommended when you want to draw a different taste than usual.
The figure below is drawn with a tadpoles pen from line drawings to painting (no processing)

水彩境界が入った混色しないブラシです。
線画から塗りまで使えますが、普段使いには向かないと思います(思った通りの塗りになりにくいので)
逆に普段とは違う描き味が欲しくなったときにおすすめです。
下図は線画から塗りまでじゃくむらペンで描いています(加工なし)
