I guess one way to determine whether the M6 with KL6 is 'worth it' is to compare the area under the output/runtime line for the M6+KL6 vs two lots of the area under under the line for the L6.I have to disagree with Al about the M6's "power" being wasted as heat. The KL6 will only draw the current it normally needs for the LED, while the dual strings of 3 cells will merely provide additional amp/hour capacity resulting in twice the run time of a standard L6.
Paladin