I've had an m50 for the last few weeks, and have been using it every day along with my Sigelei 100w. The m50 is much more comfortable to hold than the much larger, square Sigelei, and will fire everything I've thrown at it from 0.3 up. I've been using it with my Lemo and Lemo Drop as well as my Hobo v2 dripper, and have been very impressed with the quality for a device in this price range.
There is a small delay in waking from sleep, and once in a while the fire button doesn't engage when I don't push it hard enough, but that's more about ensuring you push firmly on the button. The lack of pass-through can be a pain as there have been days I've run out of battery on it, but apparently Smoktech is upgrading the m50 to 65watts with passthrough. Unfortunately it looks like this is a hardware upgrade and not a firmware update, but even with its battery shortcomings this is still a great device for the price!
Only time will tell how long it will last, but for now I'm extremely happy with my purchase.
-Treeburner