This is an absolutely amazing place to stay!
The view from the balconies (it is big enough for a chair) is truly breathtaking, incredibly unique and an absolute treat! You get a true Parisian vibe by staying at Ferdinand's.
The location in the artistic, old and authentic Montmartre is wonderful, as well as it close to everything you need; metro, buses, supermarkets, etc.
A very short walk from the apartment is Rue des Martyrs which is lined all the way with cute and authentic little shops, award-winning bakeries, great cafées etc. I would recommend it for everyone who wants a truly local and authentic experience.
Note that the apartment is on 6th floor (116 stair steps - or a free alternative to the stair master from your gym ;) ) and the kitchen is very, very basic, but perfect for shorter stays or weekend getaways.
Would definitely recommend staying here! You will not be disappointed.