We (a group of six) had a fantastic stay at this apartment. It's really well located being near the metro (2 minutes walk and so easy to get around the city, to the main stations and airport etc.). Not that you'll probably need it as the main touristy areas only a short walk away (Porto's very walkable).
The apartment is spacious. It has three well sized rooms (two doubles and a twin) and easily enough room for at least six people. The views from the balcony are great; you get a good view of all the port houses and can even hear the Taylor's peacock in the morning!
Communicating with Telmo is very easy. You can use the cafe Wifi below the flat and at the airport to WhatsApp him in advance too to arrange a meeting time.
Overall I'd definitely recommend this as a place to stay.