If you can, talk to fishguy2727, He is a Vet tech/biologist and he knows the science behind NLS and why it's better than other types of foods.
Betta's may like blood worms better, but that doesn't mean it's what's best for them.
My Mbunas LOOOOVVVE blood worms, but they should never have them. That high amount of raw protein can kill them. But they love them so much they will literally eat them until they pop.
Give the NLS a try. Just buy a small jar and if after a few weeks you don't see big difference in the general health and color of your Betta. Then try something else.
I'm confident you won't change. It awesome food, no matter which type you get. The pellets come in an array of sizes so you can get the size best suited for your fish.
The NLS grow is only 0.5mm and the NLS Betta is 1mm. But NLS has food for extra large and another for Giant fish that looks about the size of dog food. I never checked the size I just saw how big it was.