Trouble with tempered glass is its lovely and nice while its in perfect condition. A single chip can in effect cause the entire block/table to break, however, break safely into chunks.
You can do some reading about the manufacturing process here:
http://en.wikipedia.org/wiki/Toughened_glass
its all about the stress and how you stress the surface. Monitor stand would distribute the weight better and will be stable, while a stand like the LX will have a small gripper that focuses the stress at a very small position and also the arm is constantly straining the mount because it is suspended, if you can imagine.
think about the pin
http://en.wikipedia.org/wiki/Pin
if you enlarge the needle point it becomes harder to penetrate surface, but the reason why pins work is because stress is focused on a tiny area,
Monitors are light, agreed, but I wouldn't want to place (in your case 8.5kg) suspended from glass.
padded?, same problem. but perhaps, if you have 2 10mm thick plank of wood, each of 300~400mm length and about 150~200mm width, you can use these to try to to distribute the weight to a larger area, radiating away from the centre of the clamp
\/\/\/\/\/ --> top teeth of clamp
========= -> 10 mm thick plank of wood
---------------- -> glass table
========= -> 10 mm thick plank of wood
\/\/\/\/\/ --->bottom teeth of clamp
you get the idea, not sure but using 2 A4 polycarbonate sheets instead of the wood would look better and may do the trick, there about 7 quid on auction sites ...
Hope this helps, but I would stick with a stand
