We (two colleagues) stayed at Lucas' place for two nights in September. Great location, very central, clean, with all you need for a short stay in Madrid. Even though we never met Lucas, our phone and email communication went smoothly, and he made sure we felt welcome at his place by arranging for someone else to meet us at the apartment.
The only downside (but only if you are carrying too much luggage, like we did) is the fact that the building has no elevator, and the apartment is situated on the top floor. We were aware of this before we arrived, though; it took some effort to carry the heavy bags all the way up, but, other than that, we highly recommend both - Lucas as a host and his apartment!