What a lovely place to stay. It's a bit out of the way from the main Paris attractions, but the metro station is close enough to get to the Louvre, Eiffel Tower, etc (it'll take like 30-40 minutes by metro). It's also about a 20 minute walk from Oberkampf, where there's plenty of great food.
The apartment itself is spotless and features a lot of modern touches. The bath tub is enormous and it's quite relaxing to unwind in it after a long day of walking around. Just be careful to not splash since there is no door (which isn't as problematic as you would expect). But I think my favorite part of the whole place was the little roof terrace. Nothing quite beats going to the market for some bread and cheese and then eating it on top of the roof.
Lastly, Valentin was a great host that quickly answered any of our questions and checked in from time to time.