Me and my brother had an excellent stay there. We weren't exactly sure what to expect considering it's an apartment serviced by a hotel, so just to clear things up, it's just like renting out an apartment, except there is a small reception room on the 2nd floor, and a few amenities are shared (microwave, washing machine, vacuum).
Our trip was complicated, but we could always count on the apartment to make ourselves feel comfortable and at home. The bed is very big and comfortable, and you can install up to two futons on the tatami space near the TV. The air conditioner is a wonder.
There are a few downsides to acknowledge however. Some might mind the lack of an elevator (it's on the 5th floor). The sound insulation is very poor, which is expected in Japanese buildings, but it's located near major roads with heavy traffic, even at night. I'd advise bringing earplugs and maybe eye masks. Last, some minor everyday items were a bit lacking (esp. kitchenware) or awkward to plug in.