Josephine's place is beautiful, it's in an absolutely great location and we had a great stay in Paris. It takes just a few minutes to get down to the river and a few more to get to Notre-Dame, for example. We even did walks to the Louvre and the Eiffel Tower and if you get tired in that direction you can just catch the metro - there's a station basically just across the street from the apartment.
The neighbourhood seems perfect, as it's not too crowded with tourists or even traffic, but it's beautiful and you're still close to all the must-visit locations. So many great cafes and restaurants, too (have to highlight Patrol for cocktails & food, Burgart for burgers & Strada for coffee and breakfast, for example).
The apartment itself is plenty spacious for 2 people and has most amenities you can think of. No AC, mind you, though my understanding is that this is normal for Paris.
The reason I took off one star on value is just because I remember picking this as one of the more (or even most) expensive spots, but it has a few spots where it can be just slightly polished - e.g. the door lock was difficult at times, the shower handle seemed to have jiggly bits, a few minor things like that. And the pillows were of the kind that feel like they're not there when you lay your head down, but this can of course be personal preference.
Overall, a beautiful place in a great neighbourhood. If the price works for you, I'd say go for it.