Xavier's flat was in a great location and suited us pretty well for a 2-month stay in Paris. There are some pros and cons but overall it's a good value and we really appreciated how responsive Nicolas was before our arrival and throughout our stay.
Things to be aware of: it's a courtyard apartment, which - especially in winter - means it's pretty dark most of the time. It's a Paris apartment so size is obviously at a premium, but the bathroom and kitchen are both pretty cramped, especially the WC. Storage, especially in the kitchen, also takes a bit of effort to make work.
On the other hand, the location is superb. 11e is super walkable and the apartment is pretty much in the middle of it all. There are at least 3 bakeries within a 5 minute walk, two or three grocery stores, a great coffee shop (Beans on Fire), a cute park, and several Metro stations. The courtyard means the apartment stays quiet - we only really heard neighbors once or twice in two months. The kitchen is pretty well equipped, the dishwasher and clothes washer work, and there's a clothes drying rack.

For a shorter stay, I think this is a perfect spot. For a longer stay, it'll work, just know you might need to come up with some workarounds!