I can't believe I'm saying this to the master of gravity, but I disagree with your comment about gravity shield :p That is a very effective shield, particularly in PvE, though it suffers somewhat in PvP due to the prevalence of rush decks there.
On the topic of this new shield, I really like the idea. It's costed appropriately, and gives a useful, but not overpowered, secondary effect in reducing direct damage dealt to the player.
As for the part about asking whether the damage is dealt in increments or in one bunch, it doesn't really matter because that's probably extremely easy to change in code if this shield or something like it ever made it into the game. I've done a bit of programming, and the part of the code that deals with that is probably smaller than the length of my post.