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That's a Majano anemone. It's considered a pest, but no where near on the scale of other pest anemones like Aiptasia.
I had one for over a year and in that time it only split once and never bothered anything. They're also easier to remove than Aiptasia as they have much tougher bodies so can be physically removed quite easily.
I'd keep it unless it's bothering anything, and get rid if it starts to split often, but they're quite pretty, so it's your call.