The other E15 thread probably has lots of info in there.
I've always liked the small 1xCR123A cell lights. The P1, and P1D became my most used in this format, but the Bitz was also a really nice while slightly larger light that I still like for it's knurling and beam. The E15 is a basic no nonsense type of light, but still offers 3 levels. Like Parnass, one of my favorite features of the E15 is the first level, simply because I can turn it on and if I need to tail stand it, it seems to run fine at that level without getting very hot at all when just sitting on the counter or desk. This is perfect for me. It's nice to use it with ceiling bounce for some late night computing or what have you.
The E15 is pretty stiff to turn, not because the the quality of the threads, but because it is a no spring light and there is a fair amount of pressure on the threads as you tighten it for on. I'm not sure yet on the long term durability of this particular crusher design, but I think Fenix would have done enough testing so I'm optamistic that it will be fine. The force may also depend on the particular battery, which is not quite as nice as it could be.
I would have prefered a slightly different tail design that is more flat and has the attachment point just on one edge like the Bitz or even just the 4 point pattern of the P1D, I have no idea why they moved to the less stable 3 point design.
Overall the light seems great, and is available at a great price point.