Ray-board vs Flat Kickboards
Flat kickboards force your arms, shoulders and neck into a highly uncomfortable position. Maintaining this position lap after lap is hard (and painful) for many swimmers. Flat kickboards create poor body alignment and head position, which encourages bad swimming form.
Ray-Board allows your arms, shoulders and neck to take a more natural posture, with your elbows bent and directly supported. The lower elbow position allows your hips and legs to achieve a more favorable alignment, and you can position your head in or out of the water to suit your training objective.