I just got my FC660M last week, I was looking at it for some time as well. I got the navy-blank version with mx reds from mechanicalkeyboards.com for $109 shipped. It's a really nice board. I was considering it and the Varmilo VA68M, but I'm not too fond of the aluminum case or the ridiculous price, so I went with this. In my experience, Leopold has the smoothest red switches, and they feel and sound even better due to the noise-dampening material that is used inside the board. I heard alot about the pad-printed legends eventually wearing down (not sure about actual longevity there), but I bought the navy blanks-version so I wouldn't have to deal with that. The stepsculpture 2 keycap profile is phenomenal and might be my new favorite profile.
The PBT is smoother than many others I have tried, but feels very high quality. All in all, a really solid board. I bought it as an answer to giving my Type-S a rest from paper-writing and wanted linear switches for more general-purpose gaming and other stuff, along with having the dedicated arrow cluster. The feet are fine, for me anyway. I usually let my board lay flat anyways while using a Heart 60% wood wrist rest. The stabilizers are cherry, and some of mine need worked in still, and others are very crisp, or becoming more crisp with use. Caps lock on this board can be switched to left ctrl (which I love and is part of the reason I bought this, too), but no, not an FN key. I would have to look but I think you can turn left the left windows key into an FN key.
Anyway, hopes that helps in some way.