I also want to get the FK. It seems like it has a shape more similar to mice like the WMO 1.1 and Sensei, which is extremely comfortable for me. I am now using the AM, and while I can use it without any issue, I really get what people say about the shape. It is not so narrow that it becomes uncomfortable to me, but in comparison , a similar mouse shape that is wider in the front feels better.
The problem is that I am overall pretty satisfied with my AM, and all in all I still find it more comfortable than all those ergonomic mice. Since the brand is not as well known and it is a bit of a niche product, I worry about resale value. I might just sick with it. Maybe wait until the inevitable FK-FG is released and get that instead.