Great location! Easily the best thing about it - easy walking distance to the Duomo and all of the sites. Can't beat the location.
The apartment itself is good - enough room for 2 couples and because of its location, you don't spend much time in the place anyway. Some minor annoyances (e.g. several door knobs would come off in your hands which was pretty funny) but the only real issue is climbing the steps each time you come in from site-seeing. If you're not prepared to climb those steps (and carry your stuff up them as well), then think hard about whether you want to stay here.
But, the location. Wow.