We've been eating mostly vegan at home for a couple of months. Coincident with that, I found an ancient jar of Marmite in the cupboard, and tried it. My mother used to eat it when I was a child, and I thought it was disgusting.
Times, and tastes, change. I finished that jar off quickly, and have been going through it like crazy since then. I know it's an acquired taste, but wow, I've been absolutely craving it. I pour a bit of olive oil on ancient-grains toast, and then slather on Marmite generously. Utterly delicious (to me, though likely few others).
I've been wanting to try Vegemite too, but it doesn't appear that anyone carries it here. EBay.ca will bring it in from Oz, the UK, or Japan, but with exorbitant associated shipping costs.
I can get Marmite at two local grocery stores, so no problem with supply.
Did a bit of research - Vitamin B12 is generally only available from animal products, but the Marmite/Vegemite yeast-based products are an exception. They're very rich in all the B vitamins, including B12.