I heard
that! Before I went to Booya Sam's LFI-II in 1989, I put rifle sights on my Mossberg 500 and set out to "zero" it from the bench with rifled slugs. By about round 5 or 6, I was starting to cry a little with every shot. The crummy rifle sights loosened up with every shot, and I stripped the threads trying to tighten them up. My entire shoulder was bruised/discolored for a week after.
When I actually attended the class, I learned that NONE of that was necessary. I learned how to shoot the gorram shotgun with hardly any recoil effects at all, and had NO pain, bruising, or discomfort in my shoulder. AND I found I could put five rifled slugs in a group the size of my hand at 50 yards with just the front bead!
Between the class tuition, travel expenses, ammo, hotel, and food, I had a bit over a grand in that class (1989 dollars), and it was among the best money I ever spent!