They are very strong. I glued a little metallic clip to my bedside table, and if I take my magnet off in the night I just reach over and it jumps onto the clip. I keep all of the others in a safe place.
Placed on a table with assorted objects, the magnet will move and attract "things". I have two layers of tape on my uncoated one..it helps with the handling. If it does crack the tape holds any pieces and prevents them from flying thru the air, etc. Once the thin nickel coating is breached, I'd not use that one anymore. They are crumbly inside I've found.

Pieces that crack off can go into your eye... so handle carefully.

I found one large strong magnet enough for me. I have some tiny ones I use on fingers/toes. It was one of those I used on my broken toe. Those are less likely to cause serious accidents, but they can fall off and get lost in the house.