Yes, it is a famously polarizing taste, but a small amount in something hefty like a ragout adds umami without adding too much of the marmite flavour. I'm vegetarian, and find it's really handy for adding meatiness to such things.

If you try it and like it, do try marmite spaghetti.

I'm less familiar with Marmite but believe it's like Vegemite, which I am VERY familiar with and love. If you don't like the taste by itself, try it as a salty additive to meat pies. Not enough to make them taste like Vegemite but just a nice heavy flavour that fills out the taste. It's great.