Anyone looking into this one? It's availability is good in EU as we speak and the price is "doable".
http://www.techpowerup.com/reviews/Fractal_Design/Kelvin_S24/
I was looking forward to this for my M1 as well, however it seems that the pump noise is quite significant. This is the only video I could find with it running, it's in German but you can get an idea of how the pump sounds:
pump at 12v: https://www.youtube.com/watch?v=fg_cx9PBaIo#t=179
pump at 9v: https://www.youtube.com/watch?v=fg_cx9PBaIo#t=227
Also keep in mind that the pump was resting on a table and was not mounted in the case so results might vary.
However, if you're not interested in extending the loop, a Corsair 100i might be a better fit since it's both cheaper and the pump is quieter (the idea is that while you might be able to change the fans if you find them annoying, there is no way to change the pump in an AIO, as far as I can tell).