These markers are really worth it, if you like this technique you'll dispose of so many colors it's incredible. Plus, they're starting to be refillable, the nib in each marker is reversible and you can find spare nibs too. I find optimum price for the quality. Only downside, the strong smell, but let's remember they're alcohol markers so it's kind of normal: better to be used in ventilated places.
They require a certain learning curve to create gradients and blending and they need to be used on ...