Both are acceptable practice, so is splitting it and putting some in primary and some in secondary... Some of us always do one, some always do the other. It's a matter of taste, I guess.
Some ferment the fruit right from the outset by putting it in primary. Some ferment the fruit gently in secondary so as not to blow off any delicate flavours or aromas. Some don't even let the fruit ferment, they stabilize a traditional mead and then add fruit to it. And some people put fruit in primary to get the fermented flavour and then stabilize and add more to get the unfermented fruit flavour with a little sweetness.
I almost always ferment on the fruit because I find it easier to manage a bag of fruit in my primary bucket, and also generally I like how it changes the taste, and if I wanted to drink wine or mead with fruit juice, I'd just mix it with juice and save myself the trouble of dithering with a fruit bag or loose fruit in secondary. I do often add spices in secondary though, I find I get better extraction with less sugar and more alcohol than I do in a sweet must.
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