Is this a good script to open a GUI?

The answer is no.

By 'opening a gui' I assume you mean to be able to see it? A GUI has a property of Visible controlled by a boolean (Yes or no)

So to 'open' a gui you'd need to use;

script.Lighting.PlayerGUI.Visible = true

and to 'close' the gui you'd need to use;

script.Lighting.PlayerGUI.Visible = false

If this is not what you meant, do tell me.

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