Me and friend of mine stayed in "the Sleep Well Amsterdam" apartments during our trip to Amsterdam on March'15. We found correct way to get the place from Amsterdam Centraal station quite fast - according to Tips on site. Beautiful Marielle met us herself and helped to take the luggage upstairs. The district is very quite in the nights, so you can really sleep well, moreover it's very close to the city center with famous bars)
Pluses: Marielle is the BEST hosts!!! The flat very clean & cosy. Absolutely everything is on place and works perfectly. Still the best apartment that I lived via the airbnb!!! Complementary coffee and tea was perfect in rainy Amsterdam those days :) Moreover Marielle left us the city map and list of "places to go" - which was very nice!
Minuses: crazy Holland stairs which lead to the 4th floor. That stairs hardly reminded us the ones that lead to the Notre dam de Paris.
Great place to stay when you are "light" traveller. I'll definitely be back to Marielle's place, when I'll come to Amsterdam next time)