Is nutritional yeast the same as baking yeast?
No. It is deactivated and will not raise anything. The two are not interchangeable.
Does it contain B12?
Some versions are fortified and say so; the organic one is not. Check the tub if that is why you are buying it.
What does it taste like?
Savoury and faintly cheesy, which is why it appears in so much dairy-free cooking.
Is the large tub worth it?
Considerably, if you cook with it regularly. Keep it dry and sealed and use a dry spoon.