We stayed 4 nights at Carlos' place. My husband and I appreciated the size of the apartment (it has 3 big bedrooms, spacious kitchen and living room with tv). It was very clean and well furnished, also with staple food ingredients like salt, pepper, sugar, tea, cooking oil etc.
The apartment has good beds, good pillows and the beddings and towels smell clean and fresh.
The location is good, although you have to be prepared to climb up and down to get to the old town and inner city of Bilbao. We also appreciated that Carlos was very thorough with explaining what to see, where to eat and things to do in Bilbao. We also appreciated that we could rent his private parking space for 4 days. It was in a closed garage and we felt safer leaving some of our stuff in the car.