I have the Ego Mega Cone atty and have experienced the same "suddenly dry" conditions as Cozzicon mentioned in his review. I set it down with the cart up for a couple of minutes and it recharges the filler through gravity.
He is correct in that the amount of vapor produced by these mega atties is tremendous. It's true that a light smoker/vaper might vape themselves silly at first if they treat the mega like a standard 510. You can get into the nic OD range with numb fingertips and ringing ears pretty quickly if you vape it like a madman. It can also go through ridiculous amounts of juice in a short time.
I've successfully used a Blue Foam Dart mod with the mega cart. You will still occasionally get a dry atty when the cart begins to get low (still some juice left) but it vapes almost down to the empty point before that happens. The trick is to find the minimum foam size that seals the cart and does not leak. I used a typical small soda straw from a fast food restaurant with the BFD.