Can anyone explain to me the difference between a le wilson case gauge and a stoney point bullet comparator?
The L. E. Wilson case gauge is basically a SAAMI chamber that allows you to do what others have listed + it is very useful in setting your full size die to achieve proper shoulder bump during die set up. If you don't use a way to measure the amount of shoulder bump, you may set it back too far and a head space separation (a very bad thing) could occur after several loadings.
The Stoney Point bullet comparator is a way to accurately determine how far from the lands you are seating your bullets. If you are loading in a magazine your max length is going to be 2.260" and you don't need this. If you are loading rounds individually and using longer bullets with a longer OAL, it would be useful to you.