I don’t think it is really meant to make a difference to a wine that has already been decanted. The idea is, I think, to use it as a decanter to open up the wine as with any decanter. And then to use the plunger/valve system so there is no longer any air in contact with the wine so that it does not continue to oxidise. It is intended as a way of keeping an wine once opened in good condition over several days (up to a week to 10 days I seem to remember) and do so much better than other systems like the vacuum pumps.
The aesthetics of it are, of course, a personal thing.