A clearo is either a bottom coil where the juice is fed through the small wick in the bottom of the tank. This, if properly setup, offers a cooler feel to the vape, consistant volume and decent taste. The top coil clearo is warmer for a vape and again if working properly offers a good consistent vape, but often can't wick fast as a bottom coil (yes I know I will hear about that comment.)
I have had bottom coil clearos and top. Both have done their jobs. The best, however, has been the immersed carto tank. Again, it has to do with proper setup and use. Any method can have poor wicking causing dry hits, or flooding.
The carto works for people who liked to drip. They would drip juice onto a mesh right above the coil. The problem is that they would have to constantly drip to keep it wet. Some cartomizers used a filler material that allowed for more juice (also seen in the pre-filled that you would often buy at the store,) this allowed more juice and less filling. I personally used to take the pre-filled cartos and strip out some of the filling to make drippers.
The tank style carto systems surround the tube with juice and have a filler inside. This means that the need to drip is removed. I find that once setup and working right I get a better tasting and more consistent vape from this style, but it has taken me some time to find the right combinations of tank/ cartomizer. Is it the end all be all of vaping? Certainly not.
You can usually find an inexpensive carto-tank and a good quality carto to try it out.
Fasttech sells the X8 which I like, just don't bother with the carto that comes with it.
https://www.fasttech.com/products/0/10004956/1336002-authentic-x8-25ml-electronic-cigarette-atomizer
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It is a great tank to work with. Right now my personal favorite is the AGR using a Boge slotted carto... still finicky at times, but overall the more saturated vape I have had.
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