I had a pen/brush like this in black that literally lasted over 20 years without drying out. (Obviously it wasn't a water-based ink!) I finally threw it out a year or so ago when it got mostly used up. I need to look for another one the next time I'm in Japan. I used it occasionally to sign birthday cards and the like.I really like this video because it gives a close-up view of the tip of a Shodō brush pen in action. In addition, this video shows someone using yellow ink, which looks magnificant. (We can buy Shodō brush pens in many different colors.)
The brand name of this brush pen is Pentel (ぺんてる) and I highly recommend it for beginners of Shodō.