The flat is really perfect if you want to experience a few days in Santiago like a local. You have to walk 10min to the metro or bus station and 25min to the Centro. The people in the house are very friendly and kind.
But be aware of the fact that you are right in the City Center so if you want to sleep with open window it can get really noisy.
I would defenitly recommend the flat. And one tip try the street food especially sopapilla it tastes so goooood!