It's definitely a perfect location, if you prefer not to be in the thick of it. You're so close to the shops in Le Marais, and you have ~7 minute access to great metro and bus lines. (You're also only 12 minutes away from Canal St. Martin and my personal favorite boulangerie, Du Pain et des Idées.
That being said, there are a lot of stairs. It's a spiral staircase, and the apartment is located on the 4th floor. (If you're American, it's the 5th floor.) Definitely NOT recommended for someone who is physically unable to get up the stairs, let alone carry a heavy suitcase up.
It's a cozy apartment and perfect for 2. Not sure if I'd go here as a small family since the bed is located above the couch!