Those magnets are great. Get some of the smaller ones too. With 19 lbs pull force let alone 60 lbs you will have a hard time if your keys happen to fall through an iron grate. You will probably not be able to get the magnet through the grate.
I have a 12 lbs magnet (without hole)for EDC and its almost impossible to pull it from a steel surface if it happens to stick to it. The 60 lbs magnet may actually pull your pack to nearby steel objects or vice versa over an amazing distance. When I got mine I was really surprised how powerful they are.