RDAs are the most common type of rebuildable device you will see. They are extremely popular with ‘flavour junkies’ and ‘cloud chasers’ alike as many think they provide the best flavour and the best vapour - albeit sacrificing the convenience for the pleasure.
RDA stands for 'rebuildable dripping atomizer' and are also known as ‘drippers’. An RDA does not have a tank to hold your juice, like an RTA (rebuildable tank atomizer) does, instead they generally hold as much e-liquid as the wicks can saturate, some have a small well to hold a little extra juice, although it's nothing like having a tank. When the liquid is running low, you simply drip more onto the wick and coils then vape away. You don't have to drip after each draw, some drippers can soak up a fair bit of liquid so that you can have several decent draws before having to think about dripping some more. This will depend on the wattage you are vaping at and the amount and type of wick material you have chosen to use and if the RDA has a juice well or not.
For the purist a dripper is the way to go as you get unrivalled flavour and vapour production.
RDA’s are not for beginner vapers. You must understand how to build them safely and how to test them before usage - especially if using them with a mechanical mod. Please do you research! Vape Emporium DO NOT sell clones.