UHT milk in tetra pak is UHT milk in tetra pak. I doubt you'll taste any difference between any of the brands.
I personally think UHT milk tastes much more cooked than powdered milk, more like evaporated milk, and the fact you can make cheese with powdered milk but not UHT tells me I'm right about that. But a lot of other people seem to prefer it to powdered milk (I suspect because they add no butterfat to their nonfat milk powder). It is convenient shelf-stable ready-to-drink pantry milk, although not a mid- or long-term storage food.
And it shouldn't be costing more than $4 or $5 a gallon even now.