I've stayed in dozens of Airbnbs, and Luis' places rank up with the best (I've stayed in two; T41 and T34). His small (and cozy) but thoughtfully designed and considered apartments/flats are just right for the price and have everything you need. Great if you're solo, and still great for two provided both people are fond of each other. Three could work in a pinch, but it'd be tight.
Extremely clean, well decorated and appointed, hot shower, comfortable mattress, even hooks to hang stuff (most hosts don't realize that wall hooks are important to travelers). Further, Luis is lightning fast to respond to calls or texts if you need anything, and he's cheerfully there to help as best he can. Five stars across the board.
The only thing to be aware of is that these flats are up near the Barrio Alto/Principe Real area of Lisbon and walking up to them is a fairly steep affair. If you have a lot of luggage and/or bad knees or whatnot, consider taking the funicular to the top or hiring a taxi.