Overall, we had a great trip to Porto, but we had a mixed experience with this apartment. It was very clean, a good size for a large group, and is in a good location. The communal areas is great with a large table for everyone to sit and eat together.
The main issue we faced was with poor electricity supply. The power tripped off at least ten times during our stay (I should have known when we were shown the fuse box on arrival that this may have been an issue). We had to turn off all the air-con units in order to use the kitchen - and even after doing this we could only use the hob and toaster at once (the oven tripped the power as did using a hair dryer at the same time). Don't expect to cook a hot meal in this apartment; our brunch never made it to the table.
My second issue was the fact that we had only 2 sets of keys between 13 guests, which I don't feel is acceptable. I asked for more but never received them. In addition, you need one of the keys to be able to get out of the apartment, which I felt was a bit of a fire-safety issue.
Generally though, whenever we had a problem the team at Feel Porto were responsive and there was always someone on hand to immediately resolve any problems we had.