The main benefits of having an atomizer with a sealed post. Is that it won't let any
e-liquid escape from the bottom which makes it better for dripping.
Atomizers that are not sealed would be best for bottom feeders. Since it allows
e-liquid to be fed to the atomizer from the bottom.
The main difference between a 306 and 510. Is that the main body of the 306 atomizer is exposed (wick/coil, ceramic cup, bridge, and mesh). It also requires that you buy a specialized drip tip to fit over it. In terms of performance, the vapor produced is warmer than all other atomizers. There is a slight bit of flavor loss when it comes to these atomizers.
A 510 has a cylindrical tube surrounding the main body of the atomizer. Has slightly cooler vapor and gives better flavor (slightly noticeable).
Even though the threading is different with these two atomizers. They are interchangeable and can be used on any 510 device.