I have nothing but praise for Rina and her St Germain flat.
Rina herself was very responsive to all my queries, including all my banal questions about where to go for good coffee (my answer: not Paris!) and how to work the washing machine. Information on how to get into the apartment was pretty clear.
The apartment itself is very small - almost like a Chambre de Bonne, except it's not in the roof. I was happy as a clam there by myself, and two would be OK so long as you didn't have loads and loads of luggage, but any more than that would be a squeeze. There is no storage to speak of.
The location is great. You could literally throw a stone into the metro from the window, and the neighbourhood only gets better and reveals more the longer you stay there. I was there a week.
Now, some user notes: the apartment is up a spiral staircase one floor, so you will have to carry your bags. It has a hairdryer, washing machine, coffee maker, fridge, TV, very good internet, good heating. (If you get cold you can always turn on the towel warmer, too, which will heat the entire apartment. This says more about the size of the apartment than the towel warmer itself.) The shower is small but hot and clean.