Burgess CASS filter

I happenned to be the owner of a Burgess Optical CASS filter which does the same job as Sirius Optics' MinusViolet filter does, i.e. reduces the chromatic aberration on achromats. What is the difference between these filters? Is there a good reason why the CASS filter costs twice as much as the MinusViolet filter?

Thanks,
Levente