According to the brand, the pizzas remain the same approximate size (57 square inches) with the same crust and toppings but merely sport a different shape.
There seems to be a convenience angle in play: They're touting that new shape means you can fit more into your freezer and are just the right size and shape to fit side-by-side on most baking sheets. They can also fit in a smaller-size toaster oven than before (the shape doesn't help me so much though because I tend to cook these in a pan for a crispier crust).
Image via Totino's.