"Something about the way the coil interacts with the resin, and that it releases metal into your lungs. Is this true?"
Vaping is a great alternative to smoking (inhaling combustion products), but it is not without potential health hazards. First it is important to know exactly what you are vaping; How was the cannabis grown? Were pesticides used?) Which part of the plant was utilized? How was the concentrate extracted? Where solvents used?
Also of importance is the quality of the heating element and vaporizing device. Some vaporizers are of poor rather quality, and studies have show that metals can be released during vaporization.
I would reccomend a higher-quality vaporizer, and possibly one with an all glass or ceramic heating element. You get what yopu pay for. This is a hot topic of debate, and research is ongoing. You might also want to visit fuckcombustion.com for more information.