I've got both of them, well until I receive payment for the Ultra....then it'll go away. Don't let the 500 lumen spec of the Ultra fool you into thinking it's a tightly regulated 500 lumens. Here's a link to 880arm's review of it, including an output graph.
http://flashlightguide.com/2013/05/review-surefire-e2dl-ultra/
From a beam pattern perspective, the Ultra's hot spot is significantly larger than the Elzetta's M60's innermost spot, and on initial turn-on the output is in another league. The Ultra's spill size is significantly larger. The Elzetta's factory drop-in is only one engine option. It will work with any of Malkoff's M61 drop-ins, which have outputs up to 325 lumens, using reflectors that create a completely different beam pattern. These have a more multi-purpose spot/spill ratio, that IMHO works significantly better for typical usage.
The Elzetta high/low tailcap allows the user to select which output is generated before the light is activated, so there's no need to go through high to reach the low output. It's also not possible to accidentally get the wrong output during momentary operation.
For front pocket carry, I find the Elzetta much more comfortable due to the extra length of the Ultra and how much of it is in the pocket due to the two way clip design. The Elzetta doesn't come with a clip (and their clip has't received good reviews), but any clip for a Surefire 6P will work on it. My absolute preference is the Prometheus Surefire clip.
If the light's color temperature is important, then the Elzetta with M61 gives you the choice of cool 6000 K, neutral 4000K, high CRI 4500K, among others. I've owned two Ultras and they both offered yellow-ish spots, green-ish coronas, and rosy spill.
