I have had zero issues with mine so far....but then again, it hasn't been my daily mod (the IPV4S has that spot still). As was said, feels a bit clunky in the hand and the buttons rattle.
But for a mod that might fall in the toilet, might get left outside in my lawn chair around the fire pit, gets put in my pocket while mowing, and in any other environment where you know your favorite mod will get damaged or even just scratched up or banged up, this is a great little 100W box fir for the task. And at this price you won't find much better. I keep a pair of EFest batteries in it and the built in charger works fine (one of the batteries won't charge in my Nitecore i2 due to the contact points).
At this point I think that the mod will last and not suffer from some the issues the other models had due to the removable batteries and the design differences. Time will tell of course, but if I was stepping up from a simple ecig to a "real" mod I would be very pleased with it.