My CK-6 came bundled with a BLA interface, so I got it for a lot less than it's price new.
Quality wise, it has a couple of issues that are a bit annoying: resonant body (won't really matter if you don't touch the mic) and doesn't screw properly to the spider (it won't fall but it wobbles when moved around).
Sound is pretty decent and both the high pass filter and the pad have a noticeable effect. The mic is sensitive enough and doesn't need much gain.
Self noise is very acceptable.
I'd say the sound has a certain warmth to it and the highs are a bit reinforced. Good for low raspy voices (like mine), great for folie and useful in recording other acoustic instruments.
If it wasn't for the two issues mentioned above, I'd get a second one.