The studio is the size of a hotel room, with the added bonus of a kitchenette and pretty little balcony. The location inside the old city is perfect -- it's central to shopping and restaurants, and cabs are plentiful if you want to go to the beach, etc. In fact, I ran into someone who regretted staying at one of the big hotels on the beach, saying he preferred the historic area now that he'd seen the layout of the city.
Henry the manager was very helpful, reliable and friendly. The owner sent thorough and useful information for navigating the city before arrival. The laundry facilities were great, and the street gets surprisingly quiet at night for being so bustling all day. Bed and bathroom were comfortable and clean. A/C and hot water worked great. Travelers should have no concerns about staying at the Calle de la Moneda apartments - you won't regret it.