Diego's place uses a service called Vikey to allow people into the flat. It's a third-party website that you have to create an account for, then use your phone to unlock the door. It works fine, though I was a little wary about providing my personal details (e.g. passport scans) to a website separate to Airbnb. This might not worry you, but I figure more info in a review is better than not.
The flat itself is great! Comfy bed, nice space etc. The air conditioner is the style that has a tube to vent the hot air out the window. It works brilliantly, but is fairly noisy and not something you'd be able to fall asleep to.