I have half a dozen in different flavors, and bought at least that many more as gifts in the recent rebranding sales. I've dropped my EDC AAX more than I care to admit and it works perfectly. Of all those purchased, I've only had one DoA, but it was immediately replaced by Goinggear's great service.
Quarks have their issues.... some have greenish tints/loose threads/pre-flash, but I consider them relatively minor for what you get and will echo Outdoorsman's comments. For me, it's a small, lightweight, pocketable single cell that will run from 300 lumens to 300 hours depending upon your choice of four different battery chemistries in the world's most common battery size. Adding the long warranty, and excellent customer service (w/ US HQ), and Lego-ability/parts redundancy made it my core flashlight platform.