César met us at the door of the apartment building and spent time with us giving us local advice (from things to do to his favourite brand of wine!) and left us with a decanter of port and some pasteis de nata. Before and during our stay, César always replied quickly and was very helpful with anything which we asked.
The apartment was a 5-10 minute walk to the centre of the city, perhaps 20 minutes from the river. It was spotlessly clean, well equipped and beautifully decorated.
It is worth noting that the kitchen is quite small. It had everything we needed for what we wanted to do but if you wanted to cook a lot it might be harder. However, as food in Porto is good value and there is so much to choose from this wasn't too much of an issue!
All in all we would highly recommend César's apartment as a great place to stay if you are visiting Porto.