Diogo's place is spotless and newly-renovated. It's a wonderful studio apartment with plenty of space and one of the biggest bathrooms I've experienced in many years of traveling in Europe. There is plenty of light, the kitchen is first-rate (with a decent-sized fridge, a full-size oven, four-burner stove and a microwave). The big door opens to a terrace with plenty of room to enjoy a lovely meal al fresco.
The apartment is in the Campo Grande neighborhood, which is not central but close enough to the Metro to get you to the center of town in less than 30 minutes from the time you leave the building (it is a short walk to the stop). The location was perfect for me as I had a conference at the university, which is only a five-minute walk from the building. The building is very secure as well, with 24/7 staffed front desk. If you don't speak Portuguese, bring Google Translate - it will help you get the point across that you are an AirBnB guest!
Finally, you have to at least be aware that the entire neighborhood of Campo Grande is in the landing path of the Portela Airport. Planes come in very low and the first few times it is a bit of a surprise. The apartment is well insulated, but if you are very noise sensitive, this is not the neighborhood for you. After a few hours, you get used to the planes, and they stop landing before midnight, so it's not a huge problem. But you should be aware.
All in all, this was a great place, and I highly recommend it. Diogo is a great host and should be commended for making such a wonderful apartment available on AirBnB!