What a wonderful find! We spent 5 nights in early June with our three teenagers (2 boys 1 girl). All of us loved it, and it was absolutely perfect for us. I couldn't imagine a better location in Paris--very neighborhood-y, local feel, but very close to major tourist sites, maybe 10 mins walk from Latin Quarter and Notre Dame, near St. Paul metro stop. Great patisserie/boulangerie down the street where we got croissants/baguettes each morning.
We were exhausted from so much walking on this trip, but the stairs to the apartment didn't bother us a bit (a huge suitcase might not be much fun, but we avoid those for this reason; better to have 2 smaller ones if possible). It was great for the kids to be able to spread out in the apt and get a night off with pizza from down the street while the parents had a date night out. Much better than hotel rooms. Also a beautiful place, thoughtfully decorated and laid-out with tons of charm and interesting books. This is a family home, not a "virtual hotel" like one sometimes finds. The espresso machine was terrific--I may buy one myself!
We also really appreciated how gracious Frank and Christa were about a change in our plans. We decided to arrive a night early on the last Eurostar from London and they very nicely accommodated us though it meant meeting us at the apt at midnight. We look forward to staying here again!