So far what I think we've seen from Tosun is:
Hes got a good first touch and holds the ball up well. Hes not that fast, fast enough to be average but not enough to get in behind. He strikes the ball very well. He also passes the ball really well and seems to really want someone else to play off of to pass the ball through a defense, and Tosun is capable of doing it, but we dont have a midfielder who is as well. Hes not got the workrate of Niasse. But then again who does?
All in all, if you want Niasse, we have him, if you want someone who lacks 2 of the 3 main qualities of Niasse, but is a good team player who strikes the ball very well, we have him too. His strike rate was decent, especially considering how few chances he got to strike the ball. Id love to see him in a side without Bolaise, with Lookman in the middle, and a 2nd center mid who actually pushes forward with some semblence of an attacking lineup.
Its ironic that Allardyce wanted him, because hes a forward best suited to team play and thats the last thing BFS wanted.