They have the same tunnel size but dual view machine is better machine because it can show bags images from vertical view and horizonal view.
Single view machine has 1 generator and dual view machine has 2 generators.
Single view machines now is enough for common inspection, but some high security level places like international airports they use Dual view machines for better inspection, and also it is easy to know that dual view machines are much more higher cost products.
Single view : Government buildings, mall, hotel, factories,land transportation etc.
Dual view: airport, custom, seaport etc .