Well, I love my E2/KL1. It's become my Never Leave Home Without It/EDC light. Here's why...
1. PORTABILITY: Its size/form make it eminently pocketable, though the nifty L4 ties it in this respect. I stuff my E2/KL1 into a modified ballistic nylon .38 snubby holster slipped into a front pocket and it stays there... quietly.
2. VERSATILITY: While the L4 is a great light-up-a-room-with-a-wall-of-light flooder, the KL1 ain't no slouch, but ya gotta use the "ceiling-bounce" technique to get the KL1 to work well inside. Edge to the L4. But wait! There's more -- more than just "inside" work for my EDC light.
There's OUTSIDE work. And here's where the KL1's tight throw beam shines. It's got about 30% more throw than the vaunted L2 and nearly doubles the L4's throw. If I need to light up some ambient-light-cluttered shadows 50 ft. out during a night walk, or search the backyard for bumps in the night, the E2/KL1 is up to the task. Now, the L4's broad flood beam might be "easier" for momentarily stunning the eyes of a close-up mugger while under all-thumbs stress, but the KL1's concentrated beam can be adapted for this task with moderate practice and situational awareness. It's not perfect for those jobs where a potent incan is often better, but it gets the job done.
3. RUNTIME: The E2/KL1 (or the identical E2L) doubles the L4's runtime. For an EDC light, or a deluxe back-up, or "battery-carrier" for a more potent first-line light, that's a major advantage. If I've clocked an hour on my KL1's batteries -- and then my main flashlight's (Z2, or C2, or Peli M6) batteries die -- there's enough juice in my KL1's cells to power the latter light for a while. With the L4, it's doubtful.
It all depends on what you want the tool to do.
For my multi-task needs, the E2/KL1 (or E2L) is the perfect EDC AND back-up light. It's a compromise, but it does so many things capably and efficiently. If I had to sell all my lights but one (Oh, man! The horror!) the E2/KL1 would be the Keeper.