I stayed at the Casa400 last week (8-10 Feb) as part of a group business booking.
The hotel is clean, modern and comfortable. My room was warm despite the freezing temperatures outside.
The hotel is well located for Amstel station (though not that easy to find).
We ate in the restaurant as a large group and the food is of a good standard. The bar during busy times seems understaffed but the hotel staff work hard and provide an efficient service.
I had a good stay and I would return.