I had tried a few "cheaper" isolation type products from Amazon over the years, never buying them a 2nd time due to the fact I never noticed much of a difference. On a whim but mostly due to them being slightly on sale and returnable I tried the Iso Acoustic pucks between my bookshelf speakers and stands. I was definitely amazed by how much they improved sound quality. Immediately I noticed clearer voices, midrange, higher frequency's.. initially that is what I noticed instead of the lower frequency's that most people rave on about. The freaky part was now I could turn the volume up higher than before without losing any focus or it becoming shouty. Being able to turn the knob further helped reinforce that the improvements were not all in my head.
So while I had avoided the more expensive isolation products for the longest time due to their price and my doubts, it turned out to be one of the cheapest upgrades I've made that had a significant positive effect on sound quality. I knew I had a "little" resonance coming from between the speaker and stand but had no idea how detrimental it was to the overall sound. The pucks made me such a believer that I ended up buying the mini ones and putting them under everything. How much of a difference that made I really don't know, can't tell a difference.
I am not affiliated with this or any product/manufacturer.