I stayed 4 nights at Marta's place and felt so comfortable there I never wanted to leave! The place was super clean, simply decorated and had everything you'd need, the comfy bed mattress (not too soft) and the strong enough shower pressure were a big plus. A couple of minutes to Pingo Doce (supermarket), 4 minutes to a laundry, 7 - 8 minutes to Martim Moniz metro station, easy walk to the city centre or literally everywhere if you like walking :)
It's in a quiet residential area but in the evenings / nights, you may hear the neighbours talking loud / playing music but it didn't bother me much as they were simply having a good time too after a long day and with Marta living next to you, you'd feel safe all the time.
Above all, Marta is a great host and always makes sure you are comfortable in there.
I'd definitely stay there again when I return to Lisbon!