I'm currently using the Pro1D CPL Kenko and Hoya filter... For me the quality for both are very good.. I couldn't confirm though for the normal Kenko CPL..
Hmmm,i guess thats all you want to support, cos according to reviews,many other brands seems 'unusable'. Cos of the amount of glare,reflection,and sometimes the number of stops it reduces seem undesirable to others.