Use swim accessories instead of elliptical machines when the workout needs pool-based technique, breathing practice, body position work, kick or pull drills, or water-specific conditioning. Swim tools are the better choice when the session depends on how the body moves and feels in water.
Elliptical machines still make more sense when the user needs convenient dry-land cardio, predictable pacing, or a workout without pool access. The better choice depends on whether the goal is swimming skill or general conditioning.