We stayed at Prism Ogu for 6 nights. It's situated about 5 minutes walk from Oku Station (JR Line) - which is a stop away from Ueno Station and a couple of stops away from Tokyo Station. Generally getting around isn't very difficult by train - but it would need some getting used to at the start. Location of Prism Inn isn't central, it would still require about 20-45 minutes of travelling and changing train lines to get go the main tourist areas like Shibuya, Shinjuku, Asakusa, etc., But it isn't too big a hassle if you have time.
Overall the rooms are decent sized in comparative to Japan's standard and is clean. The room provides all the necessary items you need and the dryer/heater is a plus as it helps dry clothes quickly. Room is modern
7-11 are nearby so it's an easy walk to get anything you need. The place does not provide with filtered or bottled water in the rooms, but you can self-boil or run to 7-11 to get it.
Overall would recommend Prism Inn Ogu for big and small groups