I've been using that style of disc to cut steel for ten years, never had one explode on me. I have, however, had a bit of steel in my eye. Do wear specs.
Depends what you're cutting but one disc should last for like.. 50 M8 bolts. Don't know really. For £1.11 a disc I don't tend to keep track. The deburring flap disc will last for hundreds of bolts.
I've been using that style of disc to cut steel for ten years, never had one explode on me. I have, however, had a bit of steel in my eye. Do wear specs.