My friend and I stayed at César's place for three nights and it was a really nice stay altogether. The appartment is easy to find and centrally located so that you can walk to anywhere in the city. The bed is comfy, the bathroom is really clean and even though we did not use it, the kitchen seemed perfect. The wifi works well, so does the shower.
Moreover, César is a lovely host who take good care of his guests. He was always responding to any demand we had and gave us good tips on restaurants nearby.
The only tiny thing on the "cons" list is that the street can be noisy (especially because of the seagulls!) but I guess that´s the same anywhere in Porto so we can't really complain!
To sum up, I recommend whole-heartedly César's place!