I wasn't too sure about the Nyko Power Grip for the PS Vita 2000, but after using it for 100+ hours, I gotta say I'm quite happy with it. The battery doesn't really add any noticeable weight compared to the PS Vita 1000 grip, and the handles are more comfortable than the previous one. The Vita snaps into place pretty easily (though you have to be a bit careful to make sure the power plug lines up correctly), and once in it is very secure. I haven't had it pop out or dislodge once.
The battery itself is a bit odd, in that it takes forever to charge. I thought mine was broken when I first go it, since it seriously took like 12 hours to charge (it is faster now, but still kinda slow). But once charged, it works well enough. Adds at least a couple hours to my Vita's battery's life, enough that I haven't run out of batteries while playing since I got it. Pushing the battery life from ~4 to 6-7 turns out to be a huge deal, since now it lasts as long as my more intense play sessions.
Most importantly though, it has almost entirely removed the hand cramps I used to get from playing games after 3-4 hours, which is what I was looking for from this product. The fact that it adds 2-3 hours of battery life is ultimately just a very cool perk for me, so I don't mind the slow charging.
Highly recommended for Vita power-users (you know who you are)!