Well, Prof, did you try it? I've always done the silver slide with a magnet thing for playing around with magnets and PMs. Never tried the float in water trick. I would be concerned that the Styrofoam that he uses to float stuff would attract to your hand and skew the demo.
A few years ago, I bought from some Chinese company a bunch of rare earth (neodymium) magnets of various sizes and shapes, the cost was so little as to be almost free. They are insanely strong, you cannot pull 2 quarter sized magnets apart, you have to separate them by sliding them to the side and even that is hard. If you want to stick your lawn mower to your refrigerator, these are your magnets.
Last year I removed approximately 40 to 50 yards of that old green metal lawn edging from my flower beds and yard.
It was so old and brittle that a lot of it broke apart so I ended up with pieces of rusty metal scattered throughout the beds and yard.
I put on some canvas gloves and waved 2x2x1 neodymium magnet across the areas where I removed the edging to pick up the pieces that were left behind. Worked like a charm, even "found" a stake that I had accidentally overlooked.