A sealed center post will reduce the potential for leaking. If you're a heavy dripper they're going to leak anyway by way of the air holes in the threads, this is not the case with the .357. The seal design reduces the potential for leaking whether the center post is sealed or not. The sealed posts on the first run were machined a few thousands of an inch longer than standard center posts, the potential issue was if someone wrenched their atomizer down it could possibly push the center post up far enough to put pressure on the wiring and break the vacuum seal. The issue has been eliminated by modifying the assembly, the seal design is still exactly the same, just a slight modification with the wire routing.
I don't ever see a need to dry burn an atomizer, after a good cleaning I will pump the fire button to make sure the atomizer will heat up evenly but I won't fire the atomizer to the point that the entire coil is glowing orange. By pumping the button you can get a pretty good idea of how even the coil is heating up. If you feel the need to dry burn an atomizer because of excessive carbon build up then you're not cleaning them often enough. When a coil reaches its orange glow its hot enough to char or burn the wicking material its wrapped around. Why would you purposely want to burn your wicking material? burnt wicking does not wick juice very well.
A good cleaning with Ethanol (everclear) will keep the coil clean and also remove any build up from the atomizer in general, I would never use water. When the metal wicking materiel starts to get gunked up with coagulated juice it can no longer hold the same amount of juice as when it was new, it will start leaking. How often you should clean your atomizer will be different for everyone and depend on two things, How much liquid you vape and what juice you vape. It has nothing to do with how often you vape, it's how much liquid you vape. Heavy juices, dark juices, High VG juices and more importantly juices with high sugar content are going to clog up an atomizer pretty fast.
Thank you for your detailed answers! Regarding dryburning, I wasn't sure if that was your position on the procedure in general or if it was specific to this atty for different reasons. All clear.
A couple of more questions for you, if you don't mind:
1. I prime my brand new 306 and 510 atties by placing a carto condom on the bottom of the atty and adding liquid until it reaches the bridge (usually 12-14 drops). I let the atty sit like that for a few minutes to make sure everything is soaked up nicely. Then I turn the atty over for a couple of minutes and let the excess liquid run out, and vape away. Are there any reasons why I should not do this with the HH atty?
2. I don't have much experience with "de-bridged" atties. What's the best way use the HH? Is it better to add drops directly onto the coil or is it better to drip down the side of the tube at an agle to reach the mesh first?
Again, TIA.