We found our stay here in Marais to be very comfortable and convenient. Bert was a extremely kind host and his communication was superb. Any questions that we had were answered almost immediately, and the apartment had everything we needed - plus a small welcome gift of eggs and wine which was greatly appreciated.
Location was also excellent! We were able to walk to all of the major locations in Paris for tourism, food, shopping, etc. The metro is also right around the corner which is very convenient.
Some things to note, as others have mentioned, the apartment is a 5 or 6 flight walk-up (which we didn't mind), but carrying luggage can be a bit cumbersome. The stairs up to the loft are a bit steep as well, but there are handrails to assist. Those who are less adventurous or with disability may find issue there.
There is a portable AC in the loft which we found to be very helpful and it helped keep us cool and comfortable at night.