We stayed 6 nights at Mariana and Tomek's. Everything was perfect and very smooth, from booking to departure. They were prompt to reply, managed to have someone available for my check in event though it was quite early.
The place itself is very nice, small but convenient (we were three, it is ideal for two but three is fine) and anyway you'll spend most of your day exploring Lisbon. The location is amazing and good starting point for visiting the city.
Overall a great stay. Do not hesitate :)