I have had these over a year now and use them not only for bike forks, but really anything I don't want to mark up. The magnets on the under sides are still there and doing the job. They work perfectly, just wish they were a bit larger is all, but still no complaints.
I purchased this to hold a shaft on a shock I was rebuilding. It worked great. You could make them yourself, but these have nice machined slots in them to help grip things and magnetic strips to keep them stuck to the vise. So they really pay for themselves in convenience.