When looking at this, I looked up how to keep the fizz and the internet (so must be right!) categorically has tested the fork in the fizz to death. It has no benefit compared to leaving the bottle open in the fridge.
So I needed a "proper" solution that didn't involve guzzling the lot. This was cheap and has turned out to be a good buy. I've tried it on standard wine bottles and fizzy ones of a few different neck sizes. All seem to work to varying degrees of success but you really need a good definitive lip on the bottle top.
Once installed I've gone back a good few days later (I really must drink more!) to find the bottle perfectly fizzy still.
A good purchase once you get the knack of using it. Now, where are those olives?