We had a lovely time at Rui's & Elsa's place and recommend the place for everyone! Everything was just as described and met our expectations fully.
If you don't expect a 4-star hotel room then you will be very satisfied with the apartment. The apartment was somewhat roomier than I personally expected. Very nice space with a large fridge and a good stove.
The bed was comfortable, a bit small for me and my girlfriend since I'm 1.90m and 110kg, but manageable. The streets can be loud at nights, especially when the garbage truck comes, but it didn't really bother us.
The shower cabin's size was pretty ok, but I will say that it's much more comfortable if you're tall and skinny, and not tall and slightly chubby like me. :)
The airport transfer was a very nice touch and made our arrival very pleasant, especially since we had several connecting flights. We were welcomed at the airport by Carlos and he was great. Got some very helpful tips from him and the wine was delicious.
One tip for other travelers: if you're going to Lisbon then do watch out for pickpockets, especially in very crowded spaces with lots of people, and on the nr 28 tram. We managed to encounter both some pickpockets and drug dealers, but thankfully nothing was stolen.
I guess my overall physique and bald head was enough to scare them away. :)