How do gloves for raynaud's syndrome work and are they worth it?

Warms the hands. Yes the gloves are worth it. What the gloves do is keeping the hands warmer which decrease the incidence of the spasms of the small arteries and capillaries of the fingers and decrease the symptoms of the color changes of the hands. Just as important, is to keep the rest of your body warm. If your core temperature is warmer then the blood getting to the hands and feet will also be warmer.
Protect from cold. Protect from cold, and if fitted properly, from vibration, and they are worth it.