The KL5A is like a temporary product to fill a gap in their range.
Whether its output is 120 lumen or 100 lumens (although I'm under the impression it was same output as the KL5 but with longer runtime) - the point is that its not a new product - just an update to have something available.
I guess that for some the need to have or to know that an output is 120 rather than 100 is important. Each to their own. I'm not sure the SureFire L5 (KL5A) is the most appropriate flashlight to build such a foundation on though.