This picture from FPN user rpsyed shows how the piston stops ink flow in a Japanese ED quite clearly. And you are right, piston fillers only differ in that there is a built-in mechanism to help you draw ink into the barrel. But the compromise here is a decreased capacity, as it is often not easy to get a full fill in one shot.
No silicone grease necessary, but it can smooth the action as well as help maintain the threading of the section and barrel if you apply a thin coat. I usually apply a coat also on the end cap, since you work it every time you write. But that's just the OCD in me, not at all required. Enjoy your new pens!
And for those who are interested, I've just read
this interesting review on another modern Japanese ED the Namiki Emperor. The review has some relevant information and links on Japanese eyedroppers.
Here's another with caption
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