Aftermarket grips for the K6S are at this point not available from a number of the usual suppliers.
The K6S is all steel and weighs 23oz. vs. 22.1oz. for the all steel S&W 640 Pro. Comparing the K6S to a scandium frame S&W 340 is silly.
Retail price 640 Pro $839
Retail Price K6S $899
Used prices should equalize in a few months as demand wanes.
Size of the K6S and a 640 Pro are literally identical. What differs is the shape of the trigger guard which will determine if it will fit in your current j-frame holster. The Ruger is a much larger gun.

Kimber does offer the K6S in a high polished finish which would make it a potential scratch magnet. I personally wish they offered one in black.

K6S is probably not for everybody. Just those who seek something different from the usual offerings.