Main replacer will replace the basic Dragon Priest Staff and hence be used for all Destruction school magic staffs in your game, including the one found in Skuldafn.

A low/reduced texture set you can install after either of the above two versions to lessen any hit on lower end machines. You will notice a drop in quality but the set is very light impact.

MQ staff replacer will replace the Dragon Priest staff used to open the portal to Sovngarde found in Skuldafn. While not easy to acquire there are plenty of guides on how to out there. This will give your game a single unique version of the staff.