Basic magnetic stuff you can buy in a regular store I wouldn't worry about. I have a fairly strong magnet that I use on a string to pick up pins, I keep it stuck to one of the feet of my sewing table.
Super strong specialty magnets are typically owned by people who know what they are doing or why they have them. Or, if you've ever taken out the magnet from a computer hard drive, well, I wouldn't stick that on a computerized machine but there probably isn't enough metal in the case of the machine for a good connection anyway.