I stayed at Casa 400 for a conference, and I found that it was very well suited for the purpose. It was clean, spacious, and comfortable (with the exception of the pillows). The bathroom is modern and has a terrific shower. I found the room temperature a bit too cool for my taste (the thermostat doesn't really do much at all), but the staff were very kind and even offered to bring me a space heater if I wanted it.
The location is very close to Amstel station, which is good for public transport links. For someone coming as a tourist, the hotel is a bit of a way out of the city centre, but it is accessible by bus/tram/metro - just take note of the changes due to metro construction works going on at the moment.
There are few restaurants within a 5-10 minute walk, unfortunately. The three recommended by the reception were all quite expensive. I ate at the hotel's restaurant (Circles) one night, and while it was on the pricey side, at least the food was nice. Again, if you don't plan on hanging around by the hotel all day, it's not really an issue, as there are plenty of other restaurants in Amsterdam!
Overall, I was pleased with my stay at Casa 400, and would stay again if I have a similar function in the future.