Alot of breeders use them only, and alot of people won't fed them. I would think the chance that you are taking is not worth the bettas life or suffering. If you could find another source of food, I would recommend that. Only if you are for certain they are healthy would I fed them. I never have and don't have any personal experiences with them, but other breeders I know have tried them, and they have always had some fish die, and they believed from no other cause than feeding them live blackworms.