re a rolling magnet bar, I bought HF's $10 version.
17 In. Mini Magnetic Sweeper. Claimed 4.5 lb pulling force. The magnetism is adequate for washers, nuts, bent framing nails. On a flat floor it doesn't skip over objects that it should lift. Even when running it across a small pile of debris collected by sweeping with a broom. However - I used it on the lawn to find roofing nails dropped by the roofers and the handle-to-bar joint bent immediately. Classic Early-HF, more flimsy than you expected. Way too flimsy for anything but smooth floor, and don't hit a table leg or it will fold up. I reinforced the joint with a right-angle shelf support and hose clamps, now it's sufficient for occasionally finding a lost nut that went under the workbench etc. I recommend get one of the more expensive versions, skip the cheap one.