Why not? Prices of things will be the same with our income tax or a national sales tax.
Your premise is flawed in that you assert that things can be taxed twice under the nrst. It is at the very heart of the nrst to tax things only once.
When you take a few minutes to read the bill or a synopsis, you will see that things manufactured with income taxed goods and services will NOT pay the national retail sales tax.
So your jumping-off point was bad.
The big promise was supposedly prices would fall. "In addition, prices will drop by an estimated 20–30%" So which one is it? Will the prices fall or stay the same?
It is difficult to have a meaningful discussion with a double minded person.