We had a lovely 9-day stay at this apartment. It's extremely centrally located, which, yes, means some noise, but we found ourselves enjoying the music that would regularly waft through the windows (highlights were the violinist, the bossa nova singer, and the opera singer, though the bon jovi singer left something to be desired). By 1am or so the streets were quiet, and we never had any trouble sleeping.
For those wondering about air-conditioning in the summer: we stayed in August and were always comfortable day or night. There's a big, powerful fan as well which more than compensated for any hot afternoon.
As far as amenities, everything was super clean, the wifi never had any problems, and the vintage furniture was a lovely and functional touch. We'd definitely stay again if we're ever in Porto. Obrigada!