I think KLMX is CCA and fleks is OFC... basically OFC is "better" but testing showed very little difference between the two since the CCA is actually "oversized" and bigger than the OFC...
They rate the KLMX at 250A and the Fleks at 300A. I believe they also said that at lengths less than 20' the KLMX will perform the same as any OFC cable.