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.

@audiorusty  My understanding of the video was it measured much higher plugged without isolation feet.  Then much less with isolation feet.

He talks about why he thinks there was very little difference with/without feet unplugged...  yet a significant difference sealed with/without feet.. So to be clear:

Open ports = almost no difference in stock vs Isolation feet
Sealed = significant drop in db when using isolation feet

do the positives outweigh the negative of less output?.

@dtximages

Aye, there's the rub, for in that sound of boom what sounds may come must give us pause and make cowards of us all.

- When I die Shakespeare will surely have words for me, I'm pretty sure we'll both end up in the same dry, hot place.

I teach emotionally disturbed kids and this thread makes me feel like I'm back at work!

I'm using townshend speaker bars on my standmount speakers, on an oak floor on concrete. The stands are weighted with atacama atabites for a total mass including speakers of about 27kg each.

There is another set of 4 decoupling durometer pads on the top of the stands. The townshend are not cheap new price was about £900.

 I always buy isolation devices 2nd hand and paid £400, figuring if they did nothing I can move them on. They are entirely positive in my experience, imaging is improved bass is cleaner.

For a front firing subwoofer I would expect improvements too for sure, for down firing sub , I can imagine things could be different but I wouldn't say they don't work without trying them first. 

On my down firing REL transmission line subwoofer I replaced the stock feet with stillpoint ultra SS, I also again found improved imaging here weirdly but that might be about controlling vibrations into the rest of the room and system, or it could just be a harmonics thing, bass is cleaner.

Bang for buck these are low in my system but they are gains so I'm still very happy. I used to use spiked stands before.

Ymmv