We had a brilliant stay in Catherine and Patrick's apartment and they were fantastic hosts. We arrived a little early, but they welcomed us in, gave us a tour, some recommendations and instructions to call at anytime if we needed anything. (Embarrassingly we forgot the building access code on our first evening and had to text Catherine at 10.30pm which I felt bad about it, but thankfully she texted straight back.)
The location is great, easily walkable from bus and metro stops (and 20 euro in a taxi from gare du nord). The photos almost don't do the apartment justice - it's beautiful, stylish, super clean and has amazing light. The windows make it really soundproof, so we didn't hear anything from the street. Everything was exactly as described and it really is just next to the Pantheon, which is incredible - and also useful for navigating!
I would say that if four people are staying in the apartment, the layout is probably best for families or close friends as the master bedroom is accessed only through the bathroom or the second bedroom - it worked fine for us, but potentially a bit weird if someone is in the shower and someone is sleeping in the second bedroom as you're a bit trapped! Also, being prudish Brits we were a bit bemused by the lack of curtains/blinds over big windows, especially in the bathroom. It's actually not really overlooked, but was a bit strange to get totally naked while seeing people are walking by on the street below. However, the shower cubicle soon steams up once you turn the (excellent) shower on!
All in all, we would definitely recommend it and all four of us wouldn't hesitate to stay there again. Many thanks Catherine and Patrick!