Well, on my glass shelf rack they work a bit better than any of the Herbie's I have here.
Actually especially better for my TT.
My particular need at the time was stopping vibration etc. from affecting my un-suspended Basis 1400.
These worked nicely, stacked 2 in each corner under 50Lbs Granite. They are not interlocked, that is, the grooves on the pads are not joined together like Lego blocks. I have them stacked and not parallel to the glass edges.

I'm figuring to cancel any vibrations generated along/in the glass. This arrangement got rid of all vibration to the table. I also use a 12" down firing HSU VTF3 MKII that can excite the room pretty quickly. This worked so well I put singles under all the rest of my equipment. Again, not having the pad ridges parallel to the glass edges.
They cleaned up the bass and most of all made my table on some material finally beat my CD. It was a nice improvement all around. My system sounds killer now.
My unscientific way of checking vibration on a piece of equipment is just lightly finger tip the piece
to see if it vibrating. Never tried a stethoscope.
Mine are from Audiogon but are the same I mentioned above. I paid $12 for 4.
The 50 Lbs granite under this table sounds better than the Maple butcher block setup I was using.
You just have to tinker around with this stuff to find out. Your setup is completely different. I'm using all tubes.
Cheap enough to resell if they don't work out.
I think the cork sandwich is a necessary component for the dampening factor involved.
Wayner's hockey pucks may work very well too on your concrete floors.
Den