Yes, speaker isolation is definitely real. The puzzle in my mind is why manufacturers of good speakers don’t pay more attention to the speaker-floor interface, given the substantial sums of money that go into their products.
I’ve tried the Gaia pucks, and Nobsound springs, but I’ve found that disks of sorbothane work just as well, don’t raise the speaker as much (which, as someone noted above, is very important), don’t cause as much disconcerting wobble, look better (they're less conspicuous), and are FAR cheaper. The trick is to find the right density of sorbothane for the weight you need to support, but if you guess wrong, you can usually repurpose the disks you bought for another component until you get it right.
There are several reliable sellers of sorbothane in various sizes, shapes and densities on eBay.