As a person that generally dislikes onions, it's different - I'm not a fan of onion flavor and don't like the texture, but I know it can positively contribute to a dish for me, primarily if it's not overly prominent.

It's like seasoning, eating some seasoning alone might make it taste bad, you might dislike dishes that use it as a main flavor, but if it's just a small component of a dish it might be a good thing. I haven't had marmite, but from what I've seen it seems kinda like that, very strong offputting flavor that complements other things very well.