I have mixed feelings here. I'm a science teacher and bought these to make posters on black paper for a bit more visual interest. To that end they are just okay. The metallic ones show up well and if I was going to buy more, I'd just get the metallic set. I was let down by the red and orange which weren't opaque enough and the green which was a bit dark. I'm going to try again on kraft paper and see if I like the results more.
The crayon itself is billed as "smooth" but I'd say it feels more "slick". I handed it to another teacher to try and she said, "Eww, it's like writing with lipstick," and wouldn't use it anymore. (Most kids that tried them thought that was fun!) It's also slightly crumbly - little bits build up around the surface in contact with the paper and fall off.
I'm not sure about the watercolor aspect. They wet down easily, but it was hard to tell what I was doing on black paper. They don't smudge when dry - I like that.
When I have some more time, I'll try something more illustrative rather than just text and update my review. I'll also evaluate how long lasting they are. For now they're just kind of weird and not as opaque as some other options I've tried.