I’ve kept open bottles of the same wine from the same year in a cool dark chiller both with and without using these. I can tell you that in my experience the wine remained fresher, generally doubling to tripling the life of the opened bottle. Nor is oxidization a sudden thing, so even wine that would have lasted a week or two anyway will be less oxidized when it’s reopened.
The partial vacuum is nothing compared to the bottle before the cork is popped, but it does lower the internal pressure enough to slow down oxidization. To remove the rubber cork, you tilt the nipple in the top, and you can hear the pressure equalize, so there is definitely a lower pressure in the bottle. This is also why you never want to use this for bubbles, as the lower pressure allows more of the CO2 to leave the wine.
It’s certainly no miracle worker, but it’s cheap and it keeps the wine a bit fresher.
I haven’t used it myself, but I know some oenophiles like to use nitrogen. CO2 would be harder to get into the bottle long enough to re-cork it, and if you had a tool for pumping it in through a seal, I’d worry about the CO2 pressure causing some of the gas to mix into the wine and you might get a very slight unexpected fizz inappropriate to the taste of the wine, but that’s only a guess.
https://www.amazon.com/Private-Preserve-Wine-Preservation-Spray/dp/B0000DCS18
