A one-night stopover here gets you a marble staircase people stop to photograph mid-coffee, suites bigger than almost anything else this central, and a rooftop bar with proper skyline views. The building is new enough that everything still feels considered: heated bathroom floors, windows that block out street noise entirely, a spa with a 25-metre pool that guests swim proper laps in rather than just dip into. For a hotel with only 50 rooms, that scale of finish is rare, and it's the reason so many guests call it their favourite Mandarin Oriental in the group.
Where it costs you is consistency, not quality. The doormen and reception staff get singled out by name for genuine warmth, but breakfast service has been described as guests left ten or fifteen minutes without a drink order taken, and the pool/spa desk has been left unstaffed with no one to direct guests out at closing. The hotel restaurant is also only open for breakfast, so outside the rooftop bar and room service there's nowhere else on property to eat, which matters more here than at a hotel with three restaurants to fall back on. One guest also flagged construction noise from next door, though most stays don't mention it. None of this cancels the staff warmth guests report elsewhere in the building, but at this rate it's fair to expect it at every table, not most of them.
Book it if you want the newest, most residential-feeling luxury address in Mayfair and you're not fussy about breakfast running on time. If you want old-world grandeur and more room categories to choose from, Claridge's is the obvious comparison; if it's your only night in London and you just want a beautiful, quiet room near the Elizabeth line, this is the one worth the money.