Excellent location just steps from Municipio Metro station, ferry port, and Via Toledo. Three keys for access (street, foyer to apartments, and apartment door itself). Clean and upscale interior with kitchen & dining area, automated blackout shutters, modern bathroom, and a combination washer/dryer (one machine) capable of wash+dry, wash only, spin only, dry only, etc. Very effective air conditioning, high ceiling, nice bedding. Use of stove incurs extra fee at checkout.
Negatives: (1) You have to pick up the key from a hotel on Via Nuova Marina, near Via Duomo; not far, but can be tiring with bags in hot weather if you're on foot. Checkout is easier, as there's a convenient drop box for the keys right at the apartment; just drop and go. (2) There was a glowing light from a device (wifi? Nest-device?) on the ceiling over the bed that interfered with my sleep, but I managed anyway.
Municipio station is just 2 stops from the main train station. Really, you can connect or walk to everywhere from here. On arrival in Napoli, I walked from the train station to the hotel to pick up the keys, then to the apartment, but I only had a light bag. Others may want to take the bus, metro, or taxi. This was my second stay: first stay was in the large apartment (view of castle), second time a small studio (view of other building). I was happy with it and will probably return.