I have the fk2 aswel and the sensor is pretty good but the shell is so stiff which make the lmb+rmb hard to click imo. I prefer logitech over zowie because the material is soo much better.
Also after 1-2 hours of playing the coating of the fk2 becomes so slippery that it feels like a block of soap in ur hand
ec2 has more safe and much more comfortable shape for sure. its ergonomic shape just helps a lot with comfort and consistency. and back to #26 if s2 has better shape than ec2 most would have switched to it.