Got both (but both not new - e.g. used 4th night free when staying at Conrad Dubai last spring). All 84 luxury properties eligible, subject to the usual disclaimers. Both can also be booked online using the promo codes specified in T&Cs. Here are the links:
https://www3.hiltond3.com/rs/luxury/offers/extra-night/
https://www3.hiltond3.com/rs/luxury/...lusive-credit/
@
dalbyl: Beyond the above, there are two more I am aware of: 2.5k points without limits and 25% off in EMEA (both publicly available).