Some of those higher end hotels have their own pay2stay3 or 4NF promos on their own which are available on LHR, FHR, Prive, Virtuoso etc.

You won't be able to stack those with the Prestige 4NF 'benefit'.

Basically treat the Prestige benefit as if you have an easy to use coupon for an Expedia booking that is exactly 4NF, twice a year, that you can also burn up TYP on.

If you have any TYP cows that you are milking it's a nice way to burn them, but in pure isolation, I don't think the benefit is worth all that much since you can generally replicate it by buying hotels.com gc at discounts or using OTA coupons. (Those are all harder to do of course).

And the TYP portal is - in my experience - cramped in its selection. For the types of places we travel to, it might show 15-20% of the potential hotels. For towns/resort areas which have built their own central reservations type of systems - to keep their travel commissions in house - you might find zero hotels. This is endemic to all the bank travel portals (Chase etc.) so its not a uniquely Citi problem.