I'm a Bengals fan....don't shoot.
My take on Manziel is he is not all that much different than Collin Kapernick, or Russel Wilson. If you want to be successful with him then you are going to have to design a scheme around him. He is not an in the pocket passer and neither are those guys. People don't like to admit it, but Russel Wilson is not good, or comfortable, in the pocket. He scrambles when he doesn't need to so he can get outside and make plays. If the Seahawks asked wilson to stay in the pocket like the browns did in the second half last night they would get crushed. Kapernick went from a Super Bowl QB to benched because the current coaching staff has gotten away from the scheme that made him work.
Like the Seahawks the Browns need to commit to a solid power running game and use a lot of bootlegs to compliment it. This would do a couple things for the offense, the first being it get Manziel outside in space to more easily see his receivers, but also gives him a run pass option. It in turn will help the running game as the backside defender must stay home and not chase down run plays from the backside or else risk getting beat on the bootleg.
Things like rollouts would help because it gets Manziel outside, but also because they are easy reads normally two man route combinations to his strong side with the third option being a run. These are safe ways the Browns can set him up for success if they actually wish to try. From where he was last year to where he is now tells me he can improve at a good clip, however it is a matter of if the team wants to invest in trying to compliment him.