No quality control to speak of.... I agree with the others who said they will just break (especially if you hit an edge or thereabouts) Sort of like shooting an engine block.... Rather than weights, probably old flywheels out of stickshift cars would last alot longer (if they are steel rather than cast, but just cutting some circles in 12mm steel would be cheaper in the long run, might cost a bit more to make, but would last 10 x longer.
A caution with shooting steel tho, whatever you mount it on, have it hang loose or fixed with a downward angle, so ricochet's hit the ground, rather than come straight back at you, and definately don't angle them upward
Our rules in Oz are not to shoot steel targets from within 10 meters (for obvious reason of ricochets (getting your bullet back)