Stayed there for two nights on a business trip to Institut Pasteur.
When I arrived, I was told there was no reservation on my name - even though I personally took care of this more than 2 months in advance. They even had the e-mail correspondence with me printed out, just my final confirmation was missing (I had it on my notebook). The lady at the reception told me I can stay at least the first night, she'll block any room for me in case there is a cancellation for the following night, but I should rather try to get a room in one of the other hotels nearby.
On the next day she was very happy to let me know I could stay in the room (which I also preferred a lot due to the very convenient location, Pasteur is just a 3 minutes walk). So I went through all the chaos of canceling the other hotel I booked the night before, but finally everything was ok.
Staff was okayish helpful, though they could have helped me with the phone calls (doing them in French can be a bit of a challenge). Didn't have breakfast there.
Pro: the room was *very* spacious, especially compared to all the other hotels I've seen in Paris. Windows are very good in keeping the noise out, you can't hear the busy boulevard.