When I could use frozen or freeze dried bloodworms, they were great. I am now allergic to them, a common problem from using them a lot. There's a protein in them that bothers people, not fish.
They have a good nutritional profile - high in protein and fibre. They are a freshwater food, so not marine as
@Byron notes. I find these fly larvae (they aren't really worms) in my outdoor daphnia cultures all summer long, and they are a good food source.
I don't understand the myths about freeze dried foods. I used them for decades, and they never swelled up inside any fish that I could see. They went in and traveled through like any other food. I keep reading online that one of my favourite fry foods, decapsulated brine shrimp eggs, are supposed to be fatal to young fish. I've never had a fish harmed by them either, and I have raised a lot of really good ones with that as a supplement for the days when I can't hatch live.
Freeze dried tubifex were a staple, cheap and available in the hobby for years, and I heard the exact same critique about them.
The myth probably took root when herbivore Malawi Cichlids became super popular, in the 1980s. In their case, insect foods were bad, as they have a digestive system evolved to process higher roughage plant based foods. You don't feed lamb to a cow.
So I would ignore it. If I could use freeze dried bloodworms, I'd buy them. What brand? I don't think it matters in the least. They're probably bought from jobbers and put in containers with brand names on them.