I'm wondering the same thing. It's difficult to tell from only the highlights but from what I can tell he might not have that sprint speed once he gets going, but has very nice acceleration in small spaces. He also dribbles excellently with both feet, it's a joy to watch. Between his dribbling and the short bursts of speed he appears to move fast with the ball, much like Iniesta did when he was younger (before you toss your bananas, not saying they are similar as of right now besides that aspect). We need pace in midfield, but even if he turns out to not be a speed demon, at least he's the type of player that can shield the ball and already looks comfortable in tight spaces. This is where players like Gomes, Rakitic and Paulinho make us suffer. Too slow to get back to defend counters and bad with their back to players and in tight spaces.
He's the type of player I've been wanting us to spend money on for years, but we bought Turan, Gomes and Paulinho instead. I like having a different player like Paulinho but as a sub, not a starter. A Keita type role, one that shouldn't have costed 40mil. Coutinho was a great buy, but we needed him now, not for years....for years we've needed a player with Arthurs's qualities in midfield. I hope he turns out well, he's young and appears to be a hard worker, with his head down. Excited to see him arrive and grow, just like Dembele.