Short version: book the apartment. It's great.
Details include the many positives: excellent lighting throughout the apartment; comfortable beds; two and a half baths; plenty of storage for your clothing and groceries; a real living room (So many AirBnB's put a TV in front of a sofa and call it a living room. This one had additional chairs and occasional tables.); a Netflix subscription for your viewing pleasure; showers had decent water pressure; kitchen is adequately stocked and there is plenty of counter space to prepare meals; host provides dish soap, laundry soap, and other cleaning supplies; the building reception staff is very friendly and helpful; weekly cleanings are included for multi-week stays; the host is very responsive. There were a couple small kitchen items missing when we arrived and she was quick to provide them.
The only negatives are minor: you can hear traffic noise inside the apartment, but it's not terrible; there's no furniture on the balcony; the heating and airconditioning units, which work very well, are only in the two bedrooms. There is no unit in the main living area. Like most apartments/homes in South Africa, there is load shedding, meaning the power is turned off at times to alleviate the stress on the national power grid. However, there is an app available that tells you when and for how long the electricity will be out, making the situation much more manageable than I would have expected.
We stayed for a full month, so we got to know the apartment very well. We are also frequent travelers, so we're comparing this unit to several dozen others we've stayed in. This one ranks in the top 5%. If we return to Cape Town this is our hands-down choice.