I stayed at the apartment for a month, from mid October to mid November 2018. There were good and not so good things that I encountered during my stay that I will try to provide a glimpse of in this review.
The apartment has an excellent location. Yes, it is really in the heart of St. Germain, with lots of interesting shops, restaurants, etc close by. It is also very quiet. The street it is located on is itself quiet and the apartment is in the back of the building. The downside of being in the back of the building is that it is also a bit dark, something I probably felt more strongly because of the time of the year I visited.
The apartment needs to be equipped better, especially with a more sensible set of cooking utensils and a few more glasses and coffee mugs. I would also have been happier with a better set of chairs for the table in the kitchen/dining area and a firmer mattress for the sofa-cum-bed. Moreover, an adequate supply of bed linen and towels should be provided up front; I was able to get these eventually but the point is that one should not have to ask for them. The lighting fixtures also need attention---for example, the light directly above the stove does not work---and the apartment should also be properly cleaned between guests.
I have made the host aware of these issues and I hope that they will be fixed in due course. It may merit asking if they have been before you rent because I found that communication was a bit difficult, perhaps because several properties are being managed simultaneously. Action also takes some time so it is best to reckon with these kinds of issues before you arrive.
Overall, I would definitely consider renting the place again if the issues that I have raised are taken care of!