While the value of this signing is excellent (and underestimated by some on this forum), I still don't fully understand this signing.
He doesn't really address a glaring need, as we have youth in the midfield to back up our starters, and he isn't going to come in and displace a starter. Also, his signing more or less signals that the club does not expect Arda to feature at all, so I'm expecting him to move on in this window.
Mostly, this seems like an investment buy. If he develops into a world beater, it will have been a brilliant progressive signing, and if he doesn't break into the first team as a starter over the next two years, he's young enough and hyped enough that we will probably get most of our initial investment back anyway.
He's a really promising young talent that knows the league and has the skills to fit in to our team, so I'll reserve judgement. I'm happy to see the board getting after signings aggressively, though. I just would have preferred that money being spent on a right back and a back up forward.