We loved our stay at Renaud & Costanza's. The room is a great location - it's secluded in a quiet residential area, but still close enough to the Eiffel Tower & other key sites, that you can easily walk to central Paris (we heard birds every morning when we woke up, but still had a great view of the Eiffel Tower!). The room is small & cozy, with basic amenities. Our hosts provided very detailed instructions for accessing the building upon check-in, making the process very quick and easy. It is very secure & the neighborhood felt very safe walking around at night.
I should say, if you are the rowdy type & can't be quiet after a night on the town, I don't think this is a good place for you. The location & building are very quiet, and it seems many families live there, from what I could tell. The neighborhood is very sleepy after dark.