This large 3 bedroom fat in the heart of Bastille is in a great location. The Bastille metro is literally across the street with access to all of Central Paris and beyond.
I found Aurelie, the host to be extremely nice and willing to offer help as needed. I would recommend this flat to anyone wanting to be centrally located in Paris but there are a few caveats I need to mention about the apartment:

1. The owner lives in it full time and rents as needed (for extra cash I imagine) - this means that you are living in her space and her stuff - which is not always ideal
2. The apartment faces a busy street and it can be very noisy especially on the weekends with the windows open. They are double paned, so filter most of it when closed, but I can't imagine this in the summer with the heat and no air con or fans
3. Shower is not good - one of those plastic hose things that are added to a bathtub - which is charming if you want a bath - but not so much fun when you want a shower. Water pressure sucks too.
4. Stairs: Be prepared to climb 100 steps with bags - (don't need to say more on this - 4th floor)
5. Cost: Two of the bedrooms are tiny, one with a broken bed and sheets from the kids unchanged. I would say that the cost is too high for the value of the apartment (but this is my first Airbnb experience, so don't have alot to compare to)
Note:
I needed a gym nearby and found out that the one across the street does not accomodate day passes - so I truly missed this feature (I was told access would be possible by the gym franchise, but it turns out not ok for certain particular high end ones - like this one - but I only discovered it after I arrived

So just to conclude - I like the place. I am a business traveler and used to staying in hotels. My views are biased based on what I am used to. For most people, i would think that this is a charming, large space to hang for a few days. Aurelie keeps it clean and except for a few inconveniences, is just fine.