This blister pack contains two kinds of pencil:
First a blender. This is essentially a pigment free pencil, it is the waxy carrier for pigment and that is it. With this pencil you can smooth two (or more) colours that have already been laid down on the page and mix them together. I find this useful in many circumstances where I don't want a distinct line between colours (e.g. clouds in the sky, smoke from a chimney, flesh tones in a portrait).
Secondly, a burnisher. This gives your work a subtle sheen. It's not glossy like a varnish, but a lovely subtle shimmer. I'm particularly fond of using it where light is hitting a body of water, it really gives a lift to your work. There is a slight change in the colour/depth on the page when you add the burnisher, but it's not dramatic. I also use the burnisher with
Derwent Inktense 24 Tin range of pencils. If you lay down the burnisher on the page it is waxy enough to resist water - so with the Inktense when you create a wash of colour you can leave gaps in the wash by protecting the page with the burnisher. I'm sure this would work with
Derwent Watercolour 72 Pencil Set in a Wooden Box range of pencils too.
Sharpener and eraser are also standard Derwent quality (i.e. very high) and are an added bonus. Always handy items.