I live in the Niagara region so I get bombarded with coverage of mostly the Leafs and the Sabres. I probably have watched more games with those 2 teams than I have had the chance to of all the other teams combined. I post alot about the Leafs and Sabres because that is who I see the most.
With that said my personal opinion of Cozens is he has 3 major strengths: 1. His zone entries as you said. 2. He will almost always put forth effort. The moments of him not skating hard to completing checks are few and far between. 3. He can be a tenacious forchecker.
As others have said already, what to look out for are his 3 major weaknesses: 1.) He chases the puck and gets out of position. 2.) he takes shots when he has linemates open because he doesn't always see them. 3.) His effort over-rides his hockey sense and sometimes he'll finish that check after the puck is long gone and take himself out of the play.
I think in the long run he will be best suited at wing. He LOVES going into the corners to battle for the puck in both zones. As a center, he will leave spots open for opposing players to walk into. As a winger, that is what you WANT him to do.
As far as the 'hockey IQ', yeah, it IS an issue. Not so much "hockey IQ" but he is single minded and doesn't always recognize everything around him and is pretty much 'all gas-no breaks' with his decision making. Again, a strength as a winger, as a Centre? not so much, he'll need a responsible winger to help him out.
I have also noticed one thing that a lot of other people on the Sabres board seem to miss. The first 2 games his minutes have been limited. He doesn't make nearly as many mistakes when you don't overwhelm him with ice time. Push him out there too much and it can be an issue. He seems to be a much better play around 15-16 minutes per game and a much worse at 19-20 per game.
Watch his analytics, not just over a couple games but for the rest of the season and into next. His Fenwick, Corsi, high danger chances for-vs-against and shots for-vs-against. Those are the areas that I think shows he is much more effective at wing than at Centre.