Check on the net, there are side effects with B12 sups or injection; besides, as I said, studies after studies established that vits are more readily absorbed when found in food.
you can spread dulce flakes on your food, salads, soups etc. It has a strong taste of ocean (iodine?); can't say I like it too much.Besides, some people say that the B12 found in vegetals is not really B12 and could even prevent absorption of "real" animal B12.
I think I am gonna stick with "animal" foods known to be rich in B12: liver (can't manage beef liver but I like chicken liver paté or smoked cod liver), mackerels, sardines, salmon. Seafood is a good source too but most give me allergic reactions. And of course all meats contain some B12.