SVS Subwoofer Isolation feet. Will I lose bass?

I added the SVS isolation feet to my sealed SVS SB4000 subs a few months ago. I did not experience any noticeable change in output.
The reduced db output in the video has nothing to do with the feet or the flooring, it is because the ports are being plugged. Plugging the ports on a ported sub will change the tuning of the cabinet and thusly its output.

I thought that the test that showed the most deviation was when he used the packing foam as the mounting device.

It is my understanding that a ported cabinet is a tuned cabinet where the designer is using the cabinet vibrations and internal air pressure to help increase output and enable the sub to cycle lower. In the REW analysis, there appeared to be very little difference in output and low end extension with the three mounting methods (iso feet, packing foam, batteries) when the sub was in extended and standard modes. When the sub was in sealed mode there was very little difference between the iso feet and the batteries but a significant difference with the packing foam.

So my conclusion, though maybe incorrect is that the iso feet aren't doing a lot, at least on a concrete slab, and that the port plugs and the packing foam are changing the tuning of the cabinet in a way that reduces output and low end extension.

I believe that he did not run the test with the stock feet.

Test 1 - Iso Feet
Test 2- Packing foam
Test 3 - Batteries (ridged)