This studio has recently been renovated and is comfortable and quiet. It's location very near Port Royal RER station puts it in an interesting part of the 5th arrondisement, but also close to Bld du Montmartre which is a much less tourist-invaded and more "Parisien" boulevard than St Germaine. The studio is very small (with a "click clack" fold down bed) and I would not recommend it for two people. The bathroom too, while, clean and modern, is also very small, and I am not joking when I say an overweight person or heavily pregnant woman could probably not squeeze into the shower.
Catherine was a very helpful host, although there was a bit of a problem arranging entry as I arrived in Paris on a late flight.
All in all, the studio is a pleasant place to stay for a few days.