I love these.
I studied Art and Design for my degree, and work as a goldsmith; I do a lot of sketching and designing. I always used to use Derwent pencils, but I came across these a while ago and wouldn't use anything else now. The colours are gorgeous; you can shade from barely-there light to fully saturated; the coverage is great, they feel fantastic in the hand and on the paper; value for money is amazing and I really wouldn't swap to anything else.
And yes, the odd white layer round the coloured core really does seem to stop lead-breakages. Can't recommend them strongly enough (and the watercolour pencils are just as good, by the way.)