From what we've seen so far, it seems like miha is testing him out as the release player in midfield. He almost always looks for the direct pass to the strikers. He has good long range passing but honestly I'd like a player like Monto to take over that role and let berto have a little more freedom to run off the strikers. He can beat a player or two and he's pretty fast for a centermid.
Something to consider with a player like berto though, is that he'll probably show his qaulity more as the season goes. He's feeling out his teammates still and has no chemistry yet, he doesn't know the movements yet of his fellow mids. As he gets more comfy, he'll take on more players and go for goal more often. I think he and bonaventura will work well together in tight spaces, something I'm excited to see. I'd say another 15 goal/assist combo would be more than adequate.