As good as the adult food.
I have been feeding the adult variety to my picky, pukey seniors for a couple of years now - it is much better tolerated by the ones who have sensitive tummies, so it was an obvious choice to buy the kitten variety for our new baby cats. They had previously been given Wh!skers kitten food at the rescue centre but their poop was awful!
Swapped them onto Cosma Kitten after settling them in for a few days, overlapping with the ‘other’ brand, but it is clear that they would rather eat the Cosma!