We've got a lot of MGM steel on our range. Pneumatic carbine range, running man, static steel, pistol plates, plate racks, and more. Steel is only as good as it's manufacturer. The edges will always be harder than the middle due to welding, cutting, etc. so stacking 2, 1/2 inch plates is better than a single 1 inch plate.
The mistake many people make is shooting pistol rounds, up close, at rifle steel. Once you dent the steel with high velocity rifle rounds the pistol rounds CAN hit a dent and follow it 180 degress to come back up range. Rifle round tend to fragment and chew up the base of the stand or shield, but pistol rounds like to bounce around.
If you're shooting pistol up close, you should be using an angled or falling plate. Even then you'll be getting some splash from time to time.
+1 for MGM. Mike is a great man, and his customer service is top notch. If you have questions about steel, his website is full of information.