I had the (dis)pleasure to fly in a 737 with these seats between Madrid and Amsterdam.
I really liked the headrest, especially since I had the feeling that it could be moved higher than those on most seats. Given the fact that I am quite tall (1.95m) this is one of the few seats were I can actually use the headrest as a headrest instead of a neck rest. However, the legroom with this new interior (regular economy) was just horrible. I literally couldn't fit my legs between the seats if I was sitting straight. My knees hurt after the flight, because whenever the person in front of me moved the seat also moved a bit, causing it to bump into my knees. Legroom isn't that great in the old interior, but at least it isn't this bad.
If more and more KLM 737's are converted to this interior I might start avoiding KLM short haul in favor of AF or even Ryanair or Easyjet. The legroom there might not be better at the last two, but at least they charge you less for the same (lack of) space. Luckily I will be FB platinum soon, so I hope EC is a bit better in this regard.