30 splines are stronger than 28 that is the advantage.
The Powertrax locker works fine and is easy to install. They do make a lot of noise (snapping, banging, popping and clicking). Make sure you install it as the instructions state. I used the "track" locking springs (not the street springs) in my rear end and haven't had a problem in the 1 1/2 years it's been in the car. It's seen high 11 second passes with no problem. I have heard of a few people having problems, but I think if the unit is installed correctly they are very good (except the noise), I would not want one in a daily driver due to noise and the way they make the car handle (an absolute NO NO in rainy conditions). My car does see a 99% street duty but only in good weather and is not my daily transportation.