This is the Pentel Pocket Brush Pen that uses ink cartridges so it's refillable.
It's available for sale individually, and as a pack which contains two ink cartridges and an empty pen.
The retail price seems to be around US$10. That's quite expensive when compared to the Copic brush pen.
The refill cartridge is definitely overpriced. I'll see if I can use a syringe to refill the ink instead of buying new cartridges when it's used. The usual fountain pen reusable suction-type cartridges doesn't work here because the size is different.
The photo above shows the Pentel brush pen beside a small tip Copic brush pen. My Copic brush pen tip is worn and can no longer draw a sharp thin line — I just use it to fill black areas now.
The Pentel brush pen with its bristle tip is flexible, capable of creating thin to broad strokes. Much better than Copic brush pen whose strokes are more limited.
The ink is very black, but not totally waterproof. Strangely, when applied with Copic marker, the black doesn't run out. Just make sure the ink is dry first. It drys fast enough.
The downside is the slow flow of ink. You can't work fast with this pen. If you brush across the paper surface even at typical writing speed, you get the dry brush effect (two strokes in the middle in the photo above). I'll try some other ink in the future to see if the flow is better.
There's no bleeding across the other page, at least for the 120gsm paper I'm using.
Considering that it's going to last for a while, the relatively high price doesn't look too bad.
You can read more reviews on Amazon and Blick art materials.