When you mix up a dose of Miracle-Mineral-Supplement you end up with chlorous acid. It has a pH of around 3.5. This acid has been known to upset stomachs in some cases.
The question of strength is relative...
A standard dose of Miracle-Mineral-Supplement is abut 150 times stronger than what is used to disinfect drinking water and about 1/3 the strength used to disinfect food with a 15 second spray.