Swim training gear and elliptical machines both support fitness, but they work in different worlds. Swim training gear changes what happens in the water by isolating kick, pull, body position, breathing, resistance, or stroke feel. An elliptical machine creates a dry-land cardio session through a repeated standing stride.
The difference matters because swim training gear is practice equipment for the pool, while an elliptical is conditioning equipment for land. One helps a swimmer work on the swim itself; the other builds aerobic work without getting in the water.