An alternative that I have been using for years on a variety of bikes is a self adhesive clear vinyl product from 3M. It is marketed in different countries under different brand names, so you may have to do some local research, but it is 2 - 3mm thick and flexible. You cut it to the shape of your headlight, turn on the headlight to warm up the surface, then apply.
It is practically invisible once applied, and is reportedly very effective. I can't recall whether it has ever saved my headlight, but other off road riders have shown me theirs with small nicks from flying stones.
It is a cheaper alternative, looks better, and from all accounts is just as effective.