Flat was perfect location for us (close to the Metro and a very quick journey from Gare du Nord) and exactly what we needed (a place to sleep and store our things).
Kitchen area is quite little (but we only used that for making tea and coffee really so that was no issue) and with one bathroom for quite a few guests there was a little queue for the shower in the morning.
It was really useful that we were able to store our bags downstairs even after we'd checked out - meant we could enjoy our last day without carrying our big bags everywhere with us!