if you are just feeding them to one fish, then i would recommend getting the bloodworms that come in sheets. They are easier to break apart, IMO.
I usually just swish the food around in the tank until it thaws. Been doing it that way for about 2 months now with no ill effects. And if you get the sheets instead of the cubes, you can just break off what you need without thawing out too much.
I have heard that frozen foods loose their nutritional value once they are thawed and refrozen. I have heard that once you thaw it out, you should feed it, and not to refreeze it (got this advice from people on here when I asked about it).
HTH, your betta will appreciate the frozen bloodworms.