It appears in the cross-section view that the bottom elastomer disc contacts a piston and there is a top elastomer disc. I presume the durometer of the discs and the diameter of the piston have been modeled for different mass loadings.
The benefit of the Gaia's and others is the packaging you get to conceal what otherwise would be a Rube Goldberg arrangement we most certainly would encounter if we trialed and errored our way to a solution. They have done the design work for us and made them sturdy to be attached to speakers.
The brands with springs are doing the same thing but a spring is inherently tuned to one frequency and if you get it right, then hooray. If more than one spring, then I am not sure how they achieve their target. The Gaia's may have two different durometers, thicknesses, and diameters to spread their effectiveness across a band of frequencies.
This is my first guess based on my engineering experience.
