Well it has arrived, and I've installed it, for reference here is the
Amazon link it was on sale when I bought it for 199 (still that at time of posting)
Looks nice and solid. It's thick and has a padded foam on the top underneath some fabric. It is light weight, I'm not sure maybe some kind of particle board or something, similar to the trunk floor board pieces.
Here it is folded (it does run into some issues when folding it hits the trim, but it still folds see here for video)
Here is what it looks like from the inside, doesn't go overtop of the trunk speakers
The tracks hook onto the rear seat belt holes. It's not a great fit. I tried my darndest thinking this was made from a mould, but it doesn't seem to line up perfectly. Have to be careful here because it sat too high at first and was impacting the retraction of the rear seat belt.
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All in all I say it was a good purchase for $199. I'd say there's an improvement in cabin noise, not pressure reduction. It does eliminate some road bump noises. This is all anecdotal of course, but if you know me from my post history, I'm obsessed with this. It 100% is better than those roller covers, which I own and did nothing.
If I had to give it a rating, I'd say it's a 15% improvement in cabin noise reduction.