The Shapton HC (previously called JP, and are gray) are similar to the Pro (traditional) stones in their results. The have a more solid matrix than the white glass stones (HR).
I consider them to be the Pro stones with the glass stone technology.
I've done some blogging on all of this.
First, here's an entry discussing the different names the Shaptons use.
Second, here's an entry discussing some differences between the Pro and Glass series.
There are 3 posts showing the surface scratch marks left by all of the stones in all 3 series.