I agree with the live blackworms. I also keep wild bettas but used them on my splendens and have never run into any issues with impaction, disease or parasites. I purchase my blackworms from a reputable store and keep their water clean while they are with me.
I think it was because there was a thread on here about someone's betta dying from blackworms that has made a lot of members not like them.
White worms and grindals (particularly soil-less) are easy to culture and are good foods for adult bettas. All I have to do with my grindals and white worms is make sure their media is damp enough and give them a few pieces of dried cat food daily.