The location is very convenient for people using the Gare du Nord station; it definitely was for us since we stayed 3 nights then took the Eurostar to London after. It's a little noisy, since it's close to a large hub, and there's a police or fire station nearby - we heard sirens intermittently throughout our stay, even through the night. If street noise doesn't bother you, then it's fine - we didn't have any problems sleeping.
The studio is very spacious for two - nice kitchen with supplies, large bathroom, and large living/bedroom area. Word of warning, be prepared to take large steps into/out of the shower bathtub as it's raised. The bed is also very low and a little unstable - one of the legs kept shifting around.
For such a large main space, there was only one dim, yellow-light lamp. There was a doorway light, a kitchen light, two bathroom lights, and one bedroom lamp. It made the space feel dark and not as inviting as it could have been. Heating is managed by the building, so it was a little chilly during our stay, but we were fine with a sweatshirt.
Our main issue was poor communication. At first, Tuan-Huy and his team seemed very responsive. When I reported issues through Airsorted, I was contacted almost immediately about them. However, after I sent pictures of what I had issues with, I heard nothing back. I also got no responses when we were locked out of the apartment building - the team I called was also unhelpful, stating they could do nothing to help since it was late at night and to just wait for someone to pass by and open it for us. Tuan-Huy never replied to those problems. (We were eventually let in by a nice gentleman who lived there, and he told us that the building codes had changed that day - something the host/host service should have known about).
Overall, the location and value are decent, and if you stay when they don't change the codes then you shouldn't have any issues getting in and out of the building. It's dark but functional enough, especially if you're not staying long-term. There's a Carrefour right around the corner, which is convenient as well.