First off, let it be known I use this card on 8 chemistry. I use him in a 4-3-2-1 (very underrated formation if used properly), as my right central midfielder, NOT on the wing. If you use him in the midfield, i recommend having the "get forward" attacking instruction enabled. I use him on basic chemistry. I recommend finding a way to use him central, as his value is so much higher there as opposed to the wing, in my opinion. In my team, he complements my attacking group ( hugo sanchez temporarily, eto'o and neymar) very well. His 98 acceleration is very noticeable and usable. He is not a guy that you'd want to beat everybody in a sprint to the goal but is a master at creating space if you know how. His shooting is actually very consistent, and he is very good at making the right runs. His passing is consistent as well. The way I use him, he is a perfect box-to-box midfielder, as his strength and defending was much better than I expected. If you are on a tight budget, I would not recommend using the majority of your coins to buy Gnabry. However, if you have a loose budget and need midfield help, I definitely recommend buying Gnabry. He will not be the focal point of your team, but I could not ask for a better player at midfield. At winger, he would be okay but his sprint speed will leave a bit to be desired out wide. In my strong opinion and recommendation, find a way to use him in the midfield, where his value is so much higher. He is a very balanced player around the board.
Sprint speed (depending on if you use him out wide/chemistry, although sprint speed is less important than his very noticeable great acceleration.