I used them under my Martin Logan summits. They sounded great but the downward firing woofer sent the sound through straight to the neighbours below, so I sold them off to another summit x owner and got myself auralex which sounded fine and blocked the sound.
The one designed for summits is similar but a hole in the middle. They also have parallel bars that do a similar function, and are easier to place the speaker on as all you need to do is lean back the speaker from one side, put the bar under, repeat on the other side. No need to lift the speaker up.