For some credibility, I'm a consistent Gold 1/Elite 3 player and have been playing FUT Champs since it's birth in FIFA 17.
I played with De Rossi for about half of my weekend league, and I used him on an anchor chem style. As you can see by the squad, I use De Rossi in a 4231 on the right hand side partnered next to Emre Can. I had been using Fabinho previously. Compared to Fabinho, at least, the cards are night and day as they should be. De Rossi makes a much bigger impact on the game, you can tell he's there. I know sometimes there will be the problem of CDMs where they aren't noticeable or in the correct position, but those worries are gone with De Rossi. If your opponent is going to try and get past De Rossi, it's going to be extremely difficult for him. Compared to Emre Can (Carniball) he is the way more solid defensive player 100%. I can basically say he is the best Serie A CDM that has been released all game, probably a top CDM overall. I recommend an Anchor chem style to make him a complete CDM, but I can also see a Shadow chem style doing bits, but I have yet to try that.
If you have the coins and the team (even if you don't run a Serie A squad or have the icons, you'll probably need him somewhere down the line), I recommend you definitely complete this card. For roughly over 200k (minus that with untradeables) you'll be receiving a top CDM, as well as a Rare Mega Pack and Prime Gold Players pack.
-Pace with an anchor/shadow
-Lasts the whole game
-Good dribbling but not great
-Terrible finishing if the chance arises
-2 star skills so you can't spam La Croquetas