I used to make them! You have an authentic link on that basic website you've made that includes description and link to the Guinness widget!

At one point, approximately 1/3rd of them produced went through my hands, lol!
There are (or were) about 5 or 6 different kinds of Guiness.

This particular version is for "draught Guiness in a can"

You chill the can and the liquid expands, when it was capped it had the widget dropped in, then the guiness, then had frozen nitrogen squirted in the top.

When chilled it is under pressure. You pull the tab on the top (standard) and listen to the gas escape, when the initial gas escaped you open fully and then pour the entire can into a pint glass, running down the side to allow a certain amount of froth (head) on your pint!

The widget is a two piece ball with a hole in one of the halves. The two halves are made and stuck together with heat.

When the gas escapes, there is actually air inside the widget and under pressure because of the canning process. When the can is opened the air shoots out of the widget as it spins around inside the can, and makes the liquid aireated.

You end up pouring a pint of what seems like "draught" guinness.

But like I say, there are 5 or 6 different types of guinness. The standard draught guiness is quite gloopy. The draught can with the widget inside is like aerated water and is very easily drunk. You can literally neck the entire pint in one it is so soft going down.

Then theres the Japanese version, that comes in little 250ml bottles. The barman opens and he has a plastic syringe type device that he places over the neck and pumps a few times to aerate. The japanese love their gimicky stuff. That version was only sold in Japan.