It may be entertaining to watch and it looks like a hamster is enjoying their exercise ball - in fact it's more like a transparent plastic prison from which there is no escape. This applies to all rodents in fact, as they continually fight to escape the neverending sphere, leading to stress and possible exhaustion and heat stroke.

A wheel in their cage is the best option as they can chose to get off when they've had enough. Alternatively to let your hammy roam outside their cage, use an empty bath where they can neither escape nor fall.