Here are some direct comparison pictures of the scratch marks left by Shapton Professional and Glass stones, as documented individually here and here.

The same grits make it easier to compare, but for those without the same grits have been grouped to show their relative positions and results, as demonstrated by the 4K, 5K and 6K stones. I also compared the 15K Pro and the 16K Glass.

Full size pictures are here, here, and here.