I didn't see either movie, but I thought I saw, in a tv preview, Garner holding the sai by the handle with her index fingers wrapped around one of the guards. That is a major error in at least two important styles. I can't say no one credible does that. I just don't know any that do.
And since the guards are to catch and pin other weapons (swords, bos, etc), having a finger on the inside could quickly make the 10 base number system a problem for folks that do it that way.
To learn this weapon, look for a karate school in your area that teaches OKINAWAN weapons.