Got my hands on the CK yesterday at NAMM. Regarding the 61 key, frankly build quality is basically a YC61 with MX61 keybed. I guess a decent value. But I'd probably rather opt for the YC. I bought a YC 73 last year and have absolutely no buyer's remorse now that the CK series is out.
It's unfortunate that Yamaha is phasing drums and percussion out of these instruments. I think that's a big miss. But they're "stage keyboards" so I get it.