Hi I'm first time poster,
I recently got a FK1 from eBay, there's a big chain of sellers from San Jose, they do not specify if they retail older or newer batch but I decided to take a chance anyway. Mine came with s/n: FK201X15051038768 which is a 2015 batch and I'm really, really happy with it.
The sensor performs perfectly on my steelseries HD4 pad with setting of 800 dpi and 6/11 windows sensitivity.
I do not find the clicks hard or stiff at all, this 2015 model I got feels a slight bit softer to click than one from 2014 which I have tried from a friend before. I play some LoL with it and I'm able to spam the mouse 2 effortlessly with it. I also love where the mouse 4 side button is located, this is the first mouse I've ever used that I can actually rest my thumb perfectly over a side button while gripping it normally.
The scroll wheel is also very nice, the pressure needed to make a single scroll step is just perfect, not too loose or too resistant, the wheel click feels awesome and never scrolls accidentally while clicking.
The biggest FK1 positive for me is the size of the mouse, every mouse I've had before was too short in length so I was forced to use a claw grip which I hate because of excessive wrist/finger fatigue. I have a larger than average hand and the FK1 is longer in length than most, so my middle finger does not hang off at all and this allows me use a hybrid palm-fingertip grip which is way more comfortable than claw.
I rate this mouse 9.8/10. It would be a perfect 10 for me if it were a tiny bit wider (+0.15 inch) and weight was a tad heavier (+6g)