Swim accessories differ from rowing machines because swim accessories support pool-based skill practice, comfort, and water feedback, while rowing machines provide dry-land cardio through a seated pull-and-slide motion. One supports swimming in water; the other is a complete indoor conditioning machine.
The difference matters because swim accessories can improve breathing, body position, kick, pull, and visibility in the pool. Rowing machines are better when the goal is measurable dry-land conditioning, repeatable intervals, and a full-body cardio session without pool access.