I have had mini tanks filled for a couple weeks, not a problem. Like all the juice, keep it out of sunlight or harsh light.
In my opinion, I thought the mini was better than the cartos, however, I was using a 650 Triton battery, not a G6. But I thought the vapor and flavor were superior to a carto. If it had juice, it hit well. I found my cartos would just fade.
In your next order, get a couple of them. Stay away from the smoke color, that plastic seems to crack easier than the others, but that is sorta just base on a few others posting about them. And it's not like you are investing in a $80 russian tank thing. They are four bucks. And you will totally get your money's worth.
They do seem to hit hotter than a Triton tank, in my opinion. Juices like belgian cocoa don't tolerate the minitanks well. But Torque or Malibu and even Mystic did well in them. Give them a try.