I've stayed in dozens of Airbnbs, and Luis' places rank up with the better ones (I've stayed in two; T34 and T41). 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 very tight.
Extremely clean, well appointed, hot shower, comfortable mattress. 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 main 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. Curiously, the lock to get into the front door to the complex is about 3" off the ground (total mystery) so if stooping down is difficult, be aware of that. I've also found that Portuguese locks tend to be... fussy. Also, if you're a light sleeper, the neighbors can be a little noisy at times.