I stayed at Julien´s place for 3 nights with a friend and we absolutely loved the flat.
It is located at 4 minutes from the metro station in the quaint Montmartre and has a lovely view over Paris. The flat was very clean and had everything we needed (e.g. hairdryer and coffee machine), it was a pleasure to come back to a warm and cozy studio after a day out in the cold.
Check in and useful information were provided on time and I definitely recommend to spend a couple of days at Berthe Studio.
P.s. Loved the tiny window at the back overlooking the Sacré Coeur church :)