I thought this was a room in someone's home when I made the booking, but it's actually the loft of a hotel, and receives housekeeping the same as the hotel, so it's very clean!
The check-in time is totally flexible given that you're served by the 24-hour front desk. The receptionist this morning was also lovely, allowing me to print shipping labels for my luggage and leave them with her for the courier to pick up.
It can get a little cold at night despite there being a radiator in the room (which makes little bubbling noises quite frequently, but you get used to it), but the duvets are heavenly, so we stayed warm. Note that as it's an attic the ceilings are sloped and quite low--I was fine, as I'm just 5'7" and made a point to remember the ceiling height, but my friend was 5'11" and rather more forgetful, and bumped his head a couple of times.
Overall, amazing value for the price. Plus, the neighbourhood (Oberkampf, a 3-minute walk from the métro) is lovely, with food and bars to suit all budgets open late.