Two options are attachment type - clip and velcro. Clips are great for helmets with a strap, but helmets without an attachment point can't use them so we have velcro style bows for that. The Velcro bows will come with the helmet side velcro dot that sticks on. Be prepared to replace velcro dots as needed.
The second set of options is the bow size. The smaller size is about 4 inches across, and the larger size is about 5 inches across.