I just checked it out on the Joytech site, and note that they advertise it as leak "resistant", not leak proof.
I see them as the same, but I get what you are saying. The design of the tank is really interesting. The tank is really in 2 pieces. The base/tank is a sealed cup. The top has the airflow, and the steam connected. You screw the coil into the stem, which is part of the top, and fill the tank about 2/3rd up with liquid. Screw the top on the tank, and the coil touches the bottom of the cup, to make a connection for power.
I had one other device like that -- the VapeOnly Aura. It never leaked either, and performed decent. It just wasn't great, so we never stocked it.
The only e-liquid I've had come out of the Cubis is when I fill the tank past the Max line. Any extra comes out of the top, while you screw it down. I just fill it slightly under the line now. And... the performance is really good. It is close to the Uwell Crown for vapor and flavor.