I expect offer was actually 20% discount on any f+b purchases in restaurants/in-room-dining. So if spending greater f+b than usd125 / day then discount is better option. At Da Nang easy as a couple to spent usd200/day which saves $40/day . I'd never fvoluntarily orgo upgrade in favour of a cash adjustment/discount offer by hotel. As RA it sometimes occurs I get only 1cat upgrade to a suite and cash adjustment for missed 2cat RA upgrade if hotel has limited number of beter suites.

Issue here for me is hotel offers all guests a f+b discount in attempt to increase f+b income so not sure if offer is greater discount or std offer to all guests. As RA I just paid for my evening meal on solo stay but easily spent usd70++ per evening meal in main restaurant and could have spent far more if dining in their Michelin * restraunt. Vasicall the IC f+b is open to non-guests who don't get the f+b guests discount.