3 footers...which one?

I will be getting 2 granite slabs (18 X 18 X 1.3). My Quad 21L loudspeakers will stand on these slabs. I have zeroed in on 3 footers under the speaker spikes:

1. Herbie's Cone/Spike Decoupling Glider (brass)
2. Herbie's Extra-Thick Hush Puckies (brass)
3. Waipuna Sound Myrtlefeet- Set of 4 (tall feet for spiked components)

My main intention is vibration control and raise the speaker height. What are your experiences with these products?

Thanks,
Milpai