They are basically a cheap version of a japanese water brush loaded with various colors in the barrel of the brush.
Normally a decent quality waterbrush unloaded is $8 to $12. Add in a bottle of Dr. Martins dye and that's another $5 to $8. That's about $20 for one. This package of five PAINTASTICS waterbrushes was under $5. It's clearly a lower quality product, but they are pretty fun to play with. Below is a drawing I did with the PAINTASTICS. If you're bored check 'em out, they're pretty fun!