It is much much bigger. I can post a pic tonight if you want to see an L1 and a C3 w/ KL3 side by side. Send me an email and remind me 'cause I won't get home until fairly late.
I have both, and as soon as payment arrives the KL3HA is gone and the C3 will be going back to its regular LA. The KL3HA makes the C3 just about impossible (for me) to carry and use as a pocket light, negating the advantage of the clip and HAIII finish.
Out of 2 KL3s, 2 KL1s and 1 L1 I am hard pressed to really make out that much difference in any of them except for some being slightly more purple than others. Also, some have slightly more defined hotspots than others, but outside in the world there is no real difference in output that my eyes can tell. All of them work great for short to medium range flood/work lights, none of them compare to any of the Surefire xenon LAs past 10-15 yards (IMHO). The big advantage of the 3 cell light with a kl1 or kl3 is extended runtime.
Danny