Unfortunately I cannot confirm that kk-abc is working better than reCaptcha. I switched from reCaptcha to kk-abc a week ago, and the amount of spammer registrations on my site more than doubled (18 this week vs an average of 8 per week over the past 10 weeks).
I may still stick with it, though, b/c it's more privacy-friendly than reCaptcha and I don't like handing my user's data over to Google.