I spent a night here. It's a decent hotel if you can get a good price and I really liked the food options on the next street to the hotel.

However... there's a train line running along one side of the hotel. We were allocated a room on 16th floor on the train side (oh the perks of being a plat although we did only reserve at 5pm for same evening!) and we could clearly hear the trains passing. The trains were frequent, stopped at maybe midnight or one am and picked up again early am. Make sure to request a room on the other side of the hotel if you're bothered by noise at all.

Room was exactly as per pic above. When you enter you step into bathroom and then bedroom - you can pull a sliding panel for some privacy in the bathroom. Room is small (much smaller than CY Times Square or Namdaemun) but well designed and has storage.

Breakfast was good but busy, we were told hotel was full when we enquired about switching away from trains. I'm not sure what the deal is with breakfast, we were given vouchers when I asked. Staff were really strict about taking food outside the breakfast room.

On check in we were given 500 points plus a drink and some toiletry options (small moisturiser or ear plugs or dust mask). Parking underneath hotel was included.

I'd probably stay again if I had a short one or two night stay and got a great rate compared to either courtyard TS or Namdaemun.

A property with 572 rooms seems huge for a Fairfield. At least in the USA, most/all of them seem to have only c couple hundred rooms at most.

I'm shocked that this property's breakfast policies are permitted since most people booking it would assume that Fairfield means free breakfast for all and moreover top tier elites expect breakfast (at least in place of the welcome amenity points) in all nonresort hotels that aren't RC. [I realize that MR always had a few exceptions such as the downtown Philadelphia Marriott at Convention Center/City Center, but most of us aren't accustomed to looking for them.]

How much time must we waste doing research on such issues to stay with Bonvoy?

Still, at the usual price tag I would consider staying again. The cheapest rates are approx. KRW 75,000, and all paid rates include some kind of breakfast. The rate I booked included a Grab&Go mini breakfast consisting of a sandwich and coffee or juice. The problem is that while the breakfast buffet starts at 6:30, the Grab&Go breakfast is usually available from 7:00. I asked at check in to get the sandwich at 6:30, as I needed to leave early and fortunately they made it possible.
The hotel is just a waste of points considering that there are five other category 3 properties in Seoul which offer much better value (incl. free breakfast for Elites) at the same 17,500 points level.
Two more data points: Coming from ICN you want to take bus no 6008. The terminal station of this route is just 2 minutes walking distance away from the hotel entrance. It’s KRW 9,000 for the one hour ride. Further, the 20 minute taxi ride to GMP costs approx. KRW 16,000.