A single piece of reflective material isn’t much standing between you and possibly grievous harm, especially when it's placed low to the ground where your shoes are. The motion does help to catch the attention of drivers but it's not enough and we highly recommend adding more reflectivity to your running ensemble.
Each and every piece of reflective gear increases your chances of being seen. This is especially important when the reflective gear is based on a non-dependable and direction based light source like a headlight. Additionally, other pieces of reflective gear mean a driver is more likely to see you no matter where their eye level is at.