I should update my original post. I was thrilled by my VT250s (and the quick shipping from E-Cig City) for about a week. It was quite a step up from my Smok AL85 and I love escribe and all the customizations. I quickly realized that it was not adept at switching tanks and required quite a bit of time and fiddling with the temperature settings with a tank change. Within a week, I simply stuck with my Crown 3 and was reasonably content.
I wasn't really conscious of it at first but it seemed to require almost constant temperature adjustment, not significant changes, around plus or minus 10 degrees. I tried different tanks, different coils but it drifted so much that I thought it was simply a fact of life.
Sadly, a few days ago I plugged the mod into a usb charger and a short while later I noticed that the charging amps were zero (I configured the screen to show charging voltage and amperage when plugged in). I unplugged it and it would not fire. I changed batteries, I switched between two and three battery modes, rebooted the device with escribe, all to no avail. It is dead. Escribe can see the device and while plugged in to the computer, I can change settings, etc. But it will not fire and as soon as it's unplugged, it is a paperweight.
Luckily, a friend loaned me an SX Mini ML Class to hold me over while I acquire another mod. Using the same tank, coil, juice, etc, the SX is so completely consistent that it now makes me see how much I was constantly fiddling with the DNA. The SX fires identically every time, it took me a while to tweak it to my taste but now I never touch the settings.
I emailed E-Cig City but I realize I am passed the 14 day period, so I don't expect much of a response.
Hopefully for everyone else's sake I simply got a bad unit. It's reasonable to assume that anyone buying one would never share my experience.