I’m not at all convinced by these. Without wishing to get too geeky…
The Amazon comment is quite right that simply “spraying” in a gas like this cannot prevent future contact with oxygen, though Dalton’s Law is probably not the best reference. Even if the inert gas were significantly denser than air, you’d have to have some means of “pouring” it in, to prevent it from mixing with air as it came out of the “aerosol” (not an aerosol really, an aerosol is actually a suspension of fine particles in gas). You’d have no means of knowing that you’d successfully covered the top of the wine, as the gases are clear and colourless, and most bottles are semi-opaque anyway. But even then, a process of diffusion would immediately set in, and the gases in the remaining air in the bottle would mix with the inert mixture and come into contact with the wine. Gases of different density don’t stay separated for long - the thermal movement of the molecules rapidly overcomes gravity.
The gases are nitrogen, argon and carbon dioxide (according to the page on Amazon). These are all part of normal air, and nitrogen and argon are of almost the same density as air (nitrogen slightly less, argon slightly more). Carbon dioxide is a bit denser, but it’s still going to mix very rapidly, and you’ll just be left with air. I’m afraid that the same is true of the argon spray.
A Coravin can work because it injects inert gas and leaves the bottle sealed, so no extra oxygen gets in. Any attempt to blanket the wine in a bottle from which some has been poured is doomed, as you’ll never be able to force out the air that’s already got in, so even resealing after “spraying” in won’t work.