I've had no experience with Vampire Bats, because although in Portugal we have up to The Eclipse of Hope, Legends didn't get here for some reason.
Anyway, as a finisher I normally use Naggaroth Spearmen with unit destruction to clear a path for them.
Alluring Chosen works well in a mill deck, I've pumped it to insane amounts of power.
Black Dragon Rider and Malus Darkblade are also great finishers and they work well with each other.
Vitamin T said:
I frequently do not trigger the bats ability. They are useful just to power up slave pens. Normally you should only need to trigger them 2 or 3 times during a match, but you do need to be careful, you can easily deck yourself with them!
Finally got the Legends pack, tried out the bats and I'll have to agree with Vitamin T, you have to be careful when you use them, but they are an awesome finisher.