Me and my girlfriend stayed at Guillaume's place for a weekend.
The place was quite cozy and recently renovated - everything inside was new. I must note that it was spotless clean which made a really good impression. Although located in a bit of a bad neighborhood, it is located in a very central area and on a walking distance from the Gare de l'Est - convenient location as it is close to everything. The studio was well equipped with anything you might need, the bathroom is spacious (compared to other french airbnbs we have used) and in general we are happy with our stay. Guillaume was very helpful, always responsive, and he managed to answer all our questions with really quickly.
In general, the photos show exactly how the studio is, so there were no surprises. Just one thing to note, and the only reason why I gave 4 stars, is that the bed is indeed really close to the ceiling and it is a bit tricky getting up there with the ladder. I would say it is a good spot for smaller and younger people (like us) that are still flexible. However, getting up and down is quite a hassle.
In overall, I would recommend this place. Thanks Guillaume for the excellent service and hospitality.