Celso's place is great for multiple reasons.
First of all, it is spacious, clean, quiet and you have a kitchen with everything you need if you want to cook.
Secondly, the location is great. Indeed, it is in the centre of Lisboa. Close to the metro/tram station (5 min by foot). Close to different interesting places such as historic monuments, pont of views, shops, bars/restaurants. It is also easy to reach the main train stations to go to Sintra and Cascais.
Thirdly, Celso is very nice and welcome you with pleasure. He explains you everything you need to know about Lisboa (housing, activities, transports, ...).
If you want to share an appartement with a local, a Portuguese, it is not the place. Celso's housing is more a floor with multiple bedrooms, 3 bathrooms + toilets and 1 kitchen. But it is very calm and convenient as I described above.
Though, I recommend Celso's place and wish you to enjoy your stay in Lisboa.
Cheers