Our old mia pal Geoff Kait claims his springs provide isolation superior to that of the Townshend Seismic Pod. If you watch the video Max Townshend made (and posted on YouTube) in which he compares the Pod against the bare spring used within the Pod, you can judge the theory behind the Pod for yourself. The rubber sleeve within which the spring is placed, and the small hole in the top cap of the Pod which allows air to escape in a controlled manner, act to damp the resonant behavior of the spring.
https://www.youtube.com/watch?v=OZxi1oZfvDA&t=18s