I am still on my first carto, my fourth tank. I gave mine an extreme heat test today. High 90's today in Midwest USA, with a 'miserable index' of 110. I take the tank with me to work, and today had to make some stops after work. I left it in a full-size Chevy van, all windows rolled up, lots of glass, for two hours. I was prepared for possible leakage, so I removed it from the PV, and put it in a ziplock sandwich baggie, wrapped in a paper towel, drip tip pointed up. The slot (this is a single-slot carto) was inside the tank, a 3ml about half full.
I came back, and there was a dime-sized spot in the paper towel where the battery connector was touching it, no signs of leaks around the carto O-rings. This is about what any full carto does when I stand them up overnight after a filling.
It vaped fine, but the aluminum drip tip was too hot to take anything but very short puffs. This was with 100% PG, at 100 deg F and above, this is about as thin as it gets.
This is still on my first carto, I bought two more. I see that others have very differing results with different cartos, so I may just be really lucky, and have The Golden Carto. More when I try another one, but I will wait until this one loses flavor or vape.
Temperature extremes aside, I really like this tank. I have never had a dry hit, and it tastes good all the time. Again, this is my first tank, I have no experience to compare it to. I cannot say that it is not love at first sight, but it is working well for me.
EDIT: this is a 510 choice on the carto. I am using it on a 510-510 adapter that has two air slots.