Piutau's strength is his run-direction decision making. He has Speed, but not stand out speed. He makes a lot of metres when he runs, not because of speed but because of 'where' he runs.
Another young man moving to Europe is Colin Slade. He is a No.10 with good ball running skills. Average Goal-kicking, average general kicking play. Above average link-play with the backline. I mean he is good enough to be an All Black but like Piutau he is one of those rugby players where it's hard to tell what he is good at but when you are supporting the opposite team he is just a nuisense to your teams chances.