First, the cons. Yes, it's up a big flight of stairs and there is no lift. That's it. That's all the negative things I have to say.
For the price, this is an incredible apartment in a great area of the city. There are actually _two_ balconies, one in the lounge area and one on the other end of the apartment via the bedrooms. There is a fully equipped kitchenette with washing machine, cooker, hob, fridge freezer and microwave. There is even a Nespresso machine if that's your bag.
A/C in the bedrooms and main living space was appreciated as the weather reached 30o (C) when we were there, and there is a lovely couch and a stereo system that you can connect to with Bluetooth.
The immediate area is quiet but there is a very large well stocked supermarket only 3 minutes walk away and a choice of 2 metro stations (24 de Agosto or Bolhao) and it really doesn't take long to walk to any of the main attractions that Porto has an abundance of.
Basically, stay here. As long as you can walk up the stairs.