Location, location, location (yes, a French pun)! This apartment is almost the perfect spot for visiting and touring Paris, and I only say "almost" because of some minor issues. For the cost, you will be very hard pressed to find something better, and we were quite happy with our stay.
It's located in quite nearly the center of Paris, 1er arrondissement, and only a few minutes' walk from Ile-de-la-Cite. The balcony, while narrow, allows you to stand and overlook Rue Rivoli and the Louvre, which is amazing. It is only steps from the Seine, and both the Institut Francais and the Tour Montparnasse are visible from the bedroom window. Across the street from the building is a Metro entrance to the M1 line, which goes east to west across Paris, and a few minutes away is the M7, which goes roughly north to south. Both lines provide excellent access to many Paris sites within one train change and are only one stop from the Chatelet Metro stop, which has no less than EIGHT different lines, which is more than half of the lines in the whole system. That stop is massive though, and walking between lines can be tedious so it's usually better to change trains at a smaller station.
In the immediate area of the apartment are multiple bakeries, cafes, restaurants, and shopping, including plenty of souvenir shops both on Rue Rivoli and down near the river. There is a decent grocery store just two blocks north (G20) which makes for an easy way to buy some things for breakfast or refreshment. Really, there is pretty much everything you need within short walking distance. The restaurants tend to be a little pricier since it's in the 1er, but that's what you pay for convenience and location. If you look further out from the center of the city, you'll find the less expensive, more locally-oriented restaurants.
So, the apartment itself is good. Don't expect a brand new luxury apartment because it's a typical Parisian apartment -- a little worn and cozy. If you're expecting American-style size and new build quality, you will be disappointed, but that's an unreasonable expectation for Paris anyway. The kitchen is tiny but functional, and the clothes washer in the kitchen is a MASSIVE benefit, especially if you're visiting in the summer. We found nearly everything we needed in the cabinets upon arriving and supplemented with a quick trip to the G20 store I mentioned above. The bathroom is again functional, and the newer cabinet is nice. The shower works and has plenty of hot water, but it's a smaller European shower, not the cavernous enclosures most Americans have grown accustomed to. The bathroom only has a tiny fan so expect it to get a little humid once you use the shower. The wifi was fast and easy to connect, which was essential for planning and sharing photos back home.
The main bed was comfortable after long days of walking. Our daughter slept on the sofabed, and she said it was fine. The apartment does have an air conditioning unit, and with the recent heatwaves in Paris, that's absolutely essential. It's in the tiny hallway between the main room and the bedroom, and it's basically a rolling portable AC unit that you find in the States, though the condenser is outside on the balcony. The windows have curtains, but they aren't blackout curtains. It's a good reminder to get up and get going in the morning though!
As I mentioned, it's almost perfect, but there were a few downsides that I'll list in the interest of full disclosure. The shower enclosure didn't close fully and needed some caulking in the corner so we had to figure out how to avoid getting water on the floor after a mishap or two. With the AC unit, it can only blow one direction at a time so you either cool one room or the other. During one night that was particularly hot, the main room was warm, and I had to reorient the AC unit during the night a couple times to keep it from being too warm for our daughter to sleep. During normal days, though, it really isn't an issue. If you need neck support from your pillow, bring your own. Noise from Rue Rivoli could bother some people, especially if you aren't using the AC unit (which is noisy), but noise should be expected in the heart of the city.
Finally, the owner communicates in English and is good at responding to questions and providing information. Install WhatsApp on your phone before arriving as that's the easiest way to communicate once you're in the city -- I had trouble logging into AirBnB because the site knew I was in a different country, and I was using a new SIM in my phone that I bought there. WhatsApp is a good backup if you can't reach your AirBnB account and is very widely used in Europe.
If you're going to Paris and plan to see the city, this place is a little gem that provides a near perfect launching point and recuperation site. I hope that it serves you as well as it did us! Merci!