this is just a see through tank / e-juice holder, with a wick rather than wadding, and these come with all different types of wicks, the wicks/atomizers are usually replaceable which makes them more economical than replacing the whole unit when they wear out, such as the Ego Ce4+ , the Evod or the MT3 etc. [Note low resistance atomizers will give higher vapour production because they get hotter, but will burn out more quickly]
The Ego CE 4+ and the Ego CE4 both fill from the top.
Remove the mouthpiece by gently unscrewing then tilt at an angle and fill the juice down the inside of the clearomizer being careful to avoid the central column turning the cleartomiser slowly to allow the juice to flow evenly down into the tank , always leave a little air in the clearomizer and always fill below the top of the colum otherwise you will be getting juice into the inhilation tube . These clearomizers have a scale on the side that tells you exactly how much juice you have in milli- litres. Also they have a top wick and need to be tilted occasionally to make sure that the wick remains wet , you’ll know when you need to do this if you get a dry harsh vape.