The hardest part of setting up your tank is to wrap the perfect coil, when using a premade coil you'll get a perfect coil, every time. Premade coils are used mainly for use with an RBA (rebuildable atomizers), but can also be used with some clearomizers that utilizes an RBA base.
Have in mind that the most advanced coils are made for RDA only, they simply wont fit an RDTA or RTA. Also have in mind that most ohms are specified for single coil, when using dual coil that ohm will be reduced into half. Make sure your mod can fire the ohms your coils will get, also make sure the mod supports the wire type.