I just ordered my D4 a few days ago, so it will be a little while before I have it in my hands, but I fully agree about the Zebralights.
I've bought a number of lights before (Nitecore, 4Sevens, Fenix, Olight), but nothing I've seen or heard of combines output, runtime, reliability and practicality as well as my SC600-III's do. As a visually impaired person I need access to a lot of lumens, something I can easily carry around with me, something that easily gives me the right amount of light without blinding me, but most of all I
need to be able to rely on my flashlight. Zebralight gets this balance just right, IMHO.
The D4 will serve a niche use, but I have no illusions about it replacing the Zebralights for EDC. Perhaps I'll now start carrying a D4 and an SC600-III instead of two SC600-III's. Just to get that full blast when I need it.