Yeah, I had the same thought, that twice a day sounded a bit much.
To be clear, the testimonial was from another person, who posted at the link given. I've been using magnesium oil for rinsing and brushing my teeth, along with a calcium rinse I get from calciumtherapy.com. I figure using them together is optimal. I've only swished for 20 min. once so far, after reading the testimonial. It's strong stuff, bitter tasting (I dilute it 50/50 with water), and I think anyone who wasn't used to it would have trouble pulling with it. I think I'll swish with it 2 or 3 times a week as well as continuing to brush and rinse with it, and do my regular olive oil/COQ10 swishing other days.
There are many reports of dental improvement from using it orally.
Here's Dr. Mark Sircus for example:
"What you are about to read represents a monumental medical and dental discovery. We find out after all that the most basic nutritional substance from the sea is the most powerful and safe medical healing substance. Magnesium chloride as you will see, the same product when injected during a heart attack or stroke to save your life, can be used in a wide variety of disorders. I even use it as the best mouthwash you can imagine and it has saved my gums and thus my teeth from deterioration."
So, yeah, I feel this is well worth further experimentation!