The fiber in that tablet (and also in the food you eat) will
limit B12 passive absorption in the GI tract.

B12 in patients with intact intrinsic factor do not need restrictions on food.

But patients with intrinsic factor failure (low acid in the stomach from drugs or genetic reasons--called pernicious anemia) will not absorb B12 the regular way and then rely on passive absorption.

Studies on drugs in microgram amounts (digoxin and thyroid hormone) have shown that food and fiber present in the GI tract absorbed the drugs and prevents normal absorption. B12 falls into this category.

So I would expect the B12 in that supplement to not be 100% available to all people who take it. It is also unclear what type of B12 it is... cyano ? which is synthetic and not always metabolized to methyl form in all people, or the new active form methyl B12? (which is preferrable).

People needing B12 should therefore take it separately for best results.

Also newer studies are showing potential toxicity from high dose selenium. Today the general recommendation is 100mcg daily tops.