Rage set is a viable choice on priest alt that you wont invest too heavily, or if you dont want to focus on dps on your priest main.

Because you will heal more with rage set due to magic attack buff, which give you easier time to heal through DoT mechanics. Your alt probably isnt geared enough to compete for dps anyway, so focus more on utility isnt a bad idea. The down side is only a few % dmg lost, to priest it isnt exactly a big deal.

The biggest down side, but could be a big plus? with rage set, is the market is incredibly niche, so if you opened a nice piece for another class, you may have hard time selling them, and vice versa, if you want to buy pieces for yourself, then its equally hard.