non-ionizing radiation is a lower spectrum electromagnetic radiation
ionizing radiation is a higher spectrum electromagnetic radiation that ionizes atoms and molecules
No, "spectrum" (frequency) has nothing to do with it. Ionizing radiation is high-energy atomic particles.
but this is not a point, you say this non-ionizing radiation is harmless, if such was so than this helmet will be useless as for it to have an effect on anything in the brain it needs to create a change or interact with the brain, all this interaction might help the Alzheimer's but has effect on other parts of the brain as well. The brain has a homeostasis complex system, such alterations are by themselves dangerous.
It's actually not much more than the effect you would get from a sunlamp, a heating pad or an electric blanket. From everything I've read so far, the only difference is that it's used in a "burst mode" for relatively short intervals.