Pro: It was well heated, Ruud is a great, friendly and available host .
Con: It is nice and cosy, but we would say way too small for four guests. Sleeping space is not the big issue, it's that there is not much room to move or stretch out. Do be aware that the kitchen only has a small hot plate and microwave rather than being a fully equipped kitchen. The loft is up a set of typically Dutch stairs so if you're not young and fit, you might die trying to get your suitcases up.
It's in a quiet location close to the the Rijks and Van Gogh museum, but a 30 min walk to the Dam Square (and centre of town), so depends on your priorities.
Despite these few things, we had a lovely time in Amsterdam. We would just suggest no more than two people stay in Ruud's loft.