This apartment pretty much lives up to its ad. It's in one of the most popular areas in The Marais area of Paris. To that end, what many of the other reviews you've read have said are true. It IS on a noisy street. However, that is until everything calms down later at night and then it is quite peaceful. It didn't bother me really. What helped were earplugs. In fact, the host, Victoria, provides them on your nightstand when you walk in (so she IS preparing you)!
The unit is very clean and has all the amenities you need. However, the shower towel in the bathroom could be bigger. I didn't look for other towels in the unit but this one which was on the towel rack in the bathroom seemed like the one that was being provided. The shower is ample and very comfortable. Lots of hot and ample water.
The kitchen is modern and very clean and stocked with dishes and cookware. There is a washer/dryer in the unit and an iron and ironing board (small) in the closet. However, when checking for items before I left, I found a full-sized ironing board under the bed so check there when you go!
Check-in is easy (lock box) but trying to reach the key in the lockbox is a little difficult as it's in a mailbox you have to bend down to reach and the lockbox itself is at the back of the box. Have a flashlight to see what you're doing.
There is an elevator but it is VERY narrow. The apt is on the floor right above the lobby. It could barely fit myself and one large suitcase so, if you have multiple pieces, plan on a few trips up but no big deal. The lock on the front door of the unit is a little bit of a challenge at first but just be sure to push the door forward a bit to either engage or unlock the door. I got the hang of it and it was easy from then on.
Besides the noise, the only area for improvement or flaw is that the wood floors are very creaky. So, if you were traveling with someone, they WILL hear you walking around if they're trying to take a nap. I was traveling solo so it wasn't an issue for me. Also, there are some areas where the floor is cracked and has a few holes so if you're walking around in bare feet or socks, you could catch your foot.
Bottom line - if you're looking for location with trendy restaurants, great people watching and access to the best of The Marais and don't have a problem with noise, this is a good choice.