Eri's place was a decent space with a separate dining area from the bedroom, which is a rare find in Tokyo. The bedroom has 3 double beds so could technically sleep 3 couples, but not sure if the flat is big enough or suitable for more than one couple and you'd have to be very close friends - the bathroom (wet room with shower and bath) is right next to the living/dining room so you would be walking straight out of the shower/bath into where people could be eating, and there is nowhere in the bathroom to keep the clothes you'd change into.
The place was clean but it's an old building so it didn't necessarily feel clean, and it was stuffy when my partner and I first arrived so we had to leave the windows open to air. You can hear the trains even with the windows shut so you need earplugs if you don't want your sleep disturbed. The ceiling is very low in the bedroom so you'll need to take care if you're even a bit tall.
The main bed is very comfortable (we didn't use the other two) and there is a good storage space where you can store your luggage and hang clothing.
Eri and her co-host were prompt, polite and friendly with their messages in English and Japanese. They let us check in early as the room was already cleaned. I can't fault their service.