iPhone is easier to steal since there is no strap at all and costs more than the watch

Is it easier to fall? yes, but the magnetic connection of the official strap is pretty strong. If you’re between sizes then get larger one to have more connection strength of more magnets making contact. I wouldn’t wear that band to play sports but if you’re just going on then it should be ok. If someone steals the watch then it will lock anyways as soon as it’s off ur wrist unless someone is slick enough to keep the heart rate sensor going.