Flowlight-FS do not have a timing crystal, so the lights will fall out of sync over time, but you can get them to be in sync again by stopping and moving them. The new flowlight-FS has an accelerometer, which can tell when the light is moving (kinetic) or stationary (static). When it's in kinetic, it flashes to create the pattern, and when the light is static, it chills out (otherwise it would be annoyingly blinky when it's not moving).
The key to getting flowlight FS to match each other is to make sure they enter the kinetic or static modes at the same time.
For instance, if you are using 2x flowlight FS and stop moving them at the same time, they will both go into static mode at the same time and cycle together. When you start spinning both lights again at the same time, they will enter the kinetic mode and cycle at the same time. This effect is most obvious in the slow fading rainbow modes like rainbow or rainbow drops.
In a staff, the lights on the staff ends would naturally start and stop together, so you'll experience the effect quite well. In poi, you'll experience the effect when your poi heads start and stop together.
We hope this helps, and if you have any questions please feel free contact us!