Very cute and quaint in the middle of Montemarte, perfect for a weekend stay. Moulin Rouge is right outside so of course the nightlife is high, public transport is walking distance
It is a tiny, typical Parisian apartment so a few days is perfect for 2 people (any more and it would be slightly claustrophobic)
Be midnight it is right at the top floor so 6 flights of winding stairs welcome you - prepare for the climb with your bags.