My experience here was incredible. The room was exactly as pictured (which I think is rare in many listings), and the location was perfect. To get such a central location in Paris is normally hundreds of dollars a night, so the fact that such a lovely place was available (and came with breakfast) was a great value. Speaking of breakfast, I had been expecting a little basket of croissants and some coffee each morning, but instead, there was a full spread that changed every day. Baguettes, croissants, meats/cheeses, hard boiled eggs, pastries; cookies; yogurt; oatmeal; juice... I loved being able to pick and choose what I was hungry for that morning.
The room itself is a good size with lots of shelf and wardrobe space. There are technically two bathrooms with the room - one across the hall has the sink and shower, and a small one right next to your bedroom has just the toilet and a small sink. I'd recommend bringing a robe or decent pajamas since you will need to cross public space to use either bathroom. The setup of the apartment is great too - they draw a curtain across their personal space at night which really makes you feel like you have your own area, and you won't have to worry about accidental run-ins as you're sneaking across to the bathroom. In the mornings, the curtain is drawn back so you can enjoy breakfast with a view.
I appreciated all the extra amenities they included - not just the standard soaps/towels, but also adaptors, umbrellas, and hair dryers.
In terms of location/safety - the apartment is on the fourth floor, but note that what we consider the 1st floor in the US is considered Floor 0 - so you're really going to the 5th floor. The stairs can seem like a lot at night after walking all day, but there is a very very small elevator on floor 1 that you can use. (I wish I'd realized this before I hauled my heavy suitcase up all the stairs! I definitely made use of it when I left.) There are two locking doors before you can enter the apartment, and once you check in, you'll receive a key that gets you through the first and second doors, and then into the apartment (third lock), and then finally, you can lock your room at night with another key.
The apartment is right by Chatelet Metro station - which has connections to most of the other Metro lines (including the RER line to the airport). This makes getting around the city really easy. If you're a fan of walking, the central location means you can walk to most major sites in under 30 minutes.
The hosts themselves are lovely - I only met Agnes, and she was so great to meet and talk to. Her hospitality was impeccable, and my brief interactions with her children revealed that they were polite and quiet.
THEY ALSO HAVE A CAT! That was a huge perk for me as I missed my cats from home a lot. If you are judicious about keeping your bedroom and bathroom doors shut, then you won't ever really interact with him (though sometimes he will observe you while you eat breakfast). However, when I'd get home late at night and be in the bathroom getting ready for bed, he'd sometimes slip inside my bedroom and lay on the bed looking for some attention. He was very quiet and well-behaved, and I loved having a little company as I wound down for the night.
Overall, I loved my experience here, and I will be back next time I visit Paris.