I believe the App is supposed to be faster.
With the App and IUP, you can choose the phone you want and get credit approval in advance. When it comes time to order, you verify payment information and address and that's it.
When I ordered my 8 Plus, I went opened the App on my iPad and was directed to open the App on my phone to complete my order.
Will it work this smoothly with the iPhone X? Who knows.
Wife says my wife needs a phone now, so I may give her my 8 Plus and get myself the X. As long as I get it before Christmas, I'm good.