We didn't meet David but he gave us all the information we needed to find the flat and the key, making sure that we received everything!
He also gave us lots of good tips of how to move, where to go and where to eat :)
The flat is not "central" if you want to stay next to the Duomo but the public transports are surprisingly efficient and you can be at the Duomo in 20-30 minutes depending on tram or metro (by the way if you stay more than 2 days and like to walk, we would advise a 10tickets card rather than a 24h one).
The rooms which are on the street side can become hot on sunny days but there is a fan and you can sleep with open windows.
The bikes which come with the flat are quite old but still work. For us, they were useful to ride to the Navigli (about 1km) but we thought it was too risky to take them to go to the center (one of them had no brakes).
In all, we had a very pleasant stay and everything went smoothly, if you're looking for an affordable and comfortable place, I recommend it!