I'm open-minded here. I thought the straight damage seemed odd, since unlike the belker, they don't actually form "claws" within the victim. But suffocation may be a tad lethal at that level.
What if we borrow from this...
Constrict (Ex): A choker deals 1d3+3 points of damage with a successful grapple check against a Large or smaller creature. Because it seizes its victim by the neck, a creature in the choker’s grasp cannot speak or cast spells with verbal components.
...but rather than constrict, deal nonlethal damage?