My girlfriend and I stayed at Frederic's apartment and had a very positive experience. The apartment is quaint, as advertised, but well-decorated and felt like an authentic Parisian experience. The location is fantastic with excellent bakeries just steps away, and a major metro line just 5 minutes walk. The elevator in the building was a lifesaver as well :)
Frederic was very accommodating for our stay as we had a late arrival (around 11pm) and was quick to reply whenever we needed him. I'd strongly recommend Frederic's place for couples! Be sure to check out Pere Lachaise cemetary if you get a chance :)