They are very good...but keep them in their weight ranges or they will 'squish' (flatten) permanently.
Tho very good, I always come back to the little Vibra-Killers from LAT International myself as the best isolation I have found yet ($39 for 4). They, too, will squish under loads too heavy. But, they have a small round (maybe delrin) cup underneath that holds them firmer so they squish less easily.
The Herbie's little Tenderfeet don't isolate a whole lot I find...they are better under something other than a Turntable (fine under component pieces)