We stayed at Thomas' place in the Marais and we had a good time there. The flat is in a great area, right in front of a bus stop (great for transportation), and short walks to shopping, dining, metro, etc.
The unit was quiet and secure (for us two female travelers) and the bed was comfortable. Our only issue was the small tables next to the bed. The lamp bases were large and the table was small, so not much of an area to put things (so we just moved the lamps to the floor). Luckily there were other wall mounted reading lights that helped).
The flat has a modern feel, but not sure exactly how recently it was renovated (as there were just a couple signs of wear). It has all the basic amenities you'd need, but the stairs were tricky though. They sort of slant to the left, are very well worn and spiral up to the first floor. If you have limited mobility or lots of heavy/bulky luggage, it could be challenge.
Overall, we were happy with our stay.