I did a very quick sketch using it in some random blank spot in my sketchbook - so not a formal work at all! You can see bits of other sketches on the side. It feels slightly different to an ordinary graphite pencil, as if it is harder but still smooth to sketch with. The Medium Onyx pencil can get quite dark, but only if you press down really, really hard (the very black marks in the picture are random marks from the fountain pen, not the Onyx pencil). They come in Medium or Dark, and I think next time I place I order, I will get the Dark Onyx pencil. I couldn't seem to replicate the dark shades that other people have achieved with the medium onyx pencil, and I was pressing pretty hard. I wanted to compare what this pencil is like compared to common soft graphite ones. I haven't tried the Derwent graphites.
Pros: The point kept its shape for most of the sketch, so I will probably make this my go-to pencil for on-location sketches. I hate trying to sketch something quickly with a rapidly blunting pencil. It does smudge if you accidentally run your fingers across the drawing, but not to the same extent as a soft graphite pencil. The pencil marks erase well too.
Cons: I tried blending with a blending stick, which does smudge the marks, but doesn't quite smudge the edges of the original marks (like it would if I used a soft graphite pencil). So I ended up still seeing the original marks clear as day, with the blending around them. If I was planning to blend, I would probably take more care to do very fine cross hatching. The blending stick didn't pick up much very colour from my attempts at blending either (like it would with a soft graphite pencil). One technique recommended by very fast sketchers is to pick up colour with the blending stick and do some of the drawing with that. I probably wouldn't plan to do that so much if I were using this pencil. But these are just very minor things, really.
River near Dunedin, South Island, New Zealand