In my mind, it is PAINFULLY obvious that swallowing two of these will require surgical removal.

What I'm more interested in, actually, is what happens if you swallow just one? Are these magnets strong enough to influence / interfere with the iron in your blood?

Strong magnets are REALLY cool, and REALLY fun. The closest damn thing to magic, in my opinion. I think I'm going to go buy some of these balls before they get banned...

Iron in the blood is paramagnetic. It is not affected by magnets.

I was thinking maybe one inside you would react to outside metal like say keys or a belt or a metal chair/desk

The amount of iron in your blood is really minuscule, I don't think there's any risk there.

Good to know. My medical knowledge in this area extends in so far as my being able to say "there is iron in your blood".