To chime in afterwards, as far as I know, mecha mods work by being able to output the max voltage, which is usually 3.6 volts for an 18650. The coil can be anything from 0.3 ohm up to 3.0 ohm; it heats up at whatever wattage comes out of 3.6 volts for that resistance. For example, my 0.64 ohm coil outputs 19 watts. For a 1.0 ohm coil, I guess it comes out around 12-13 watts. It’s worth using a higher resistance coil because it puts less strain on the battery (it works at lower wattage), and drains less. If I wrote something stupid, an electrician could correct me 
The reason it’s “dangerous” is that if the fire button is accidentally pressed, it will keep heating up while firing, and well… Yeah, that’s a problem… Also, putting the battery in backwards can usually cause fireworks. But I think it’s something you can get used to, it’s a nice retro feeling
You can buy electronically protected batteries in all sizes; I bought some. However, the problem is that due to the protection, they are a few millimeters taller and don’t fit into mods. But you can put a protected 18650 battery into the place of a 21700 battery, it works, and the mecha mod is immediately “fooled” I also hid a few mechs at home in preparation for World War 3 
This is a mecha boro:
