I have the SCADA Research blood pulser (a Bob Beck type blood electrification device),as well as the Don Croft Zapper.
Here're my experiences:
With the zapper alone, I haven't gotten sick AT ALL. I normally experience flu and migrains at least once a month. On the zapper, that never happens.
With the Blood Pulser alone, I DON'T get sick either AND I have a total lack of migraines which I also suffer from. The Zapper doesn't prevent migrains, but the Blood Pulser does. I surmise it alters the blood to create the chemicals which trigger my migraines.
Pulsers are usually cheaper, and IN MY CASE, more effective than Zappers.
Try the Scadaresearch Pulser. It has 4Hz, 16Hz, 100Hz frequencies. SOTA only has 4Hz. Scada is also cheaper. More bang for the buck, friends!!
John