I'm a professional artist and I use these pens myself. I think they're great because they're essentially rollerball pens with waterproof ink in various sizes. It's like having a micron pen, but not having to worrying about wearing down the tips. Been using them for years with no issues. If ink dries out, I would just refill it with more waterproof ink...very simple. These will probably last a lifetime.
You can find them cheaper on Amazon. DO BETTER MASSDROP!!!