Wismec scares me.
Devices that have problems usually have a design defect. Like the built in battery overcharging or over discharging, the 510 being leaky, the fire button getting stuck, etc. It's usually due to a poor design decision or using cheap components.
I've seen a decent amount of Wismec failures. But they're usually not due to design, they're due to bad assembly. For that reason I will never buy a Wismec product. Outside of ego sticks, joyetech for me is also a pass.
Joyetech and Wismec in my mind, are like the budget brands you find in the bargain bin at walmart or at the dollar store. You get what you pay for.
The eLeaf Picos are the exception. I know they have a good reputation.