Starcraft – Marine Arena: Goliath multi-lock weapons system

I'm wondering if the Goliath's multi-lock weapons system is worth its money. It costs 300 minerals at the merc building.

I think the update is the same as in the campaign, and allows the goliath to fire anti-air and anti-ground weapons simultaneously. So if you are attacking air and ground at the same time, it is like you have twice the firepower, right? Or does the update just make the Goliath switch between anti-air and anti-ground without any delay?

Is there otherwise a delay between switching targets?

Is it worth the money, compared to the Goliath upgrade in the middle building, or a weapons upgrade?