The problem with magnetic hold-down is that the magnets have to be really close to the floor to have much effect. That stated hold-down force of 50Kg will be when the magnet is attached to a steel surface. Magnetic attraction decreases with the cube of the distance so you will get far less attraction when the magnets have a reasonable floor clearance of (say) 5mm.

The other problems are getting high-sided by an uneven floor - it would be really embarrassing to get your bot stuck to the floor. You will also sweep up every magnetic item on the floor and this could also high-side the bot if you pick up something large.

Japanese sumo bots use magnetic hold-down very successfully but their arenas are super flat and kept clean.