Over the past 15 years I've used nothing, loose mineral, salt blocks, and tubs and various combinations of the aforementioned. Have never noticed a lick of difference in anything except in my pocket book. Didn't have breedback problems before, don't have them now. Didn't have grass tet before, don't have it now, didn't have pinkeye before and I DO have it now!! I wonder if they're getting pinkey from the mineral??? Kinda like vaccines. I never vaccinated for anything before and never had blackleg, BVD, calf scours or abortion sprees. Since I started vaccinating I've not had blackleg, BVD, calf scours or abortion sprees.
That said, I still use crystalyx tubs (spent $6,000 on them this year - 35% of what I spend on hay a year) - high mag in spring, fly control in summer, and bovatec in winter all because they are supposed to be doing something. And they say the angus breed has a good PR group!