The most important part to me, besides no safety features obviously, is the "no regulation" part.
Meaning when you put a fully charged battery (4.2V) in a mech mod, the mech mod will fire at 4.2V. As the battery's voltage drops, that changes the voltage output to the atomizer. Meaning that within an hour or so, you're not firing at 4.2V, you're firing at 3.8V.
"Regulated" mods have the ability to step up/down according to what you set the wattage/voltage to.