No issue booking via the app.
I think I read up thread that using a visa for the temporary security charge on check in has triggered it for some who then went on to use their Amex for the statement credit.
Let us know how you go, I'm in a DT next Wednesday and plan to try it out
I think i'll just try part payment on Visa.
Admittedly I had 3 stays at Hilton in China last week and Visa payments haven't posted so there is going to be a fight on my hands there.