JK Aviars are just like KC Aviars and the Star Aviar Drivers except for the plastic. JK plastic is a softer plastic and beats in buttery smooth. It's usually best to pick one out in a store where you can fondle a few to be sure to get a soft one. Sometimes they are almost as stiff as DX. These are OK of course (and I have one), but the softest JKs are the sweetest JKs. And they really beat in beautifully.
If you haven't thrown a BB Aviar, they are beaded, big rimmed, slow putters. A little overstable, but not a lot. Most manufacturers have a clone. The classic putter IMO.