You have to call the hotel to book the free shuttle bus. The staff don't speak English very well so keep it simple. Just say "I need shuttle bus" and give them the terminal you are at. For me the shuttle arrived 10min after calling. From the international terminal, the pick up location is downstairs in front of the "Police box". People at the info desk in Haneda seem to know well where it is, it's also where the airport shuttles buses leave from and where all the taxis line up. The small hotel shuttle bus comes with a big sign saying "Haneda Inn". You can't miss it.
The entrance of the hotel is small and dingy, located on a quiet street. You have to go to the 2nd floor to check in. Staff are very friendly. Most travelers seem to be solo travelers staying one night for a layover.
The room was small but had everything it needed (TV, small fridge, AC, clothes hangers, disposable slippers, bathrobe, decent wifi). The bed was clean and relatively comfy. Not the best not the worst. Same for the pillow, a bit small and a bit hard, but good enough.
Bathroom was very clean - shampoo, conditioner, body soap, hand soap, disposable toothbrush and razor were included. Water pressure of the shower was phenomenal.
There are vending machines for drinks in the hotel and there's a supermarket just around the corner. There are microwaves in the hotel.
Breakfast was very simple (toast & jam, Japanese curry, miso soup, and corn porridge. Tea, coffee, OJ). Overall great stay!