The location of this apt is good and the building safe. The Saint Ambroise (this is located right on the northern line of the quarter) quarter of the 11th is a good location to be in my opinion. Fun, out of tourist central, but convenient to everything in Paris.
One croissant tip. After exiting the building, take a right and then your first left. You will pass a Franprix (grab a fresh squeezed oj for 1.59 Euro) and then take your first left. In a few steps is Benoit Castel. Fabulous croissants.