We stayed at week at the Lisson Grove 3 bedroom flat. The location is great. Just one or two minute walk from the Marylebone station and Bakerloo line, maybe 6 minute walk over to Edgeware Road to catch the Circle and District lines. A Tesco Express is less than a block away, and there are several pubs and take away restaurants within a few minutes walk as well. Not to mention the 5-star restaurant and bars at the Landmark Hotel.
There is secure entry into the building. We were provided with two keys with security tags for entering the lobby. An elevator is provided, as well as stairs. There was no hot tub that we could determine, as mentioned in the listing, but everything else was there.
The flat was comfortable and well-equipped. One of our criteria was to have AC in the unit, and it was there, with individual thermostats in each room. There wasn't a hair dryer when we arrived, but a message to Mr. Ramsay had one there within 10 minutes. If you're wondering about coffee, there was a Nespresso machine in the kitchen; pods can be had from the Tesco Express just down the street. The mattresses were a little flat and firm compared to what I'm used to, but we slept well after walking miles every day, so it wasn't really an issue. This flat had a king bed in the master bedroom, a double plus a single in the 2nd bedroom, and a single bed in the third, very small bedroom. The open kitchen - living area is roomy with plenty of natural light. The WiFi worked well the entire time we were there. Water pressure was great and we never ran out of hot water with 4 people sharing the 2 bathrooms. As Americans, we would have liked some ice cube trays in the freezer, but we made do for the week without ice in the flat.
There is a washer/dryer in the unit. It's a small, single unit, unlike the separate machines we're used to in the States, but it handled small loads just fine. It does take a very long time to complete a wash-dry cycle, though. Something like 5-6 hours, so plan far ahead when you need to wash clothes.
Check in and check out were easy. We messaged Mr. Ramsay when we arrived and he met us there within 10 minutes. Check out was as simple as picking up after ourselves and leaving the keys in the unit. Access to the unit from Heathrow airport was easy and straightforward. We bought Oyster cards in the Underground station at Heathrow, took the new Elizabeth Line to Paddington Station (about 35 minutes), and then the Bakerloo line to Marylebone (another 5-6 min).