I bought Martinez to my Chelsea side. He wins 9/10 tackles, but still got only 6,8 something in rating the whole season. Sold him after one season though.
He is very slow.
Ruben Neves or Sergi Samper have higher offensive upside imo. I also like Lucas Silva.
Also look into the Bender brothers or Victor Wanyama if your primary or only need from a DM is defense.
The pink elephant in the room -- Lucas Romero is probably the best DM/CM available in the game for a reasonable price.
If you want a star DM who will impact right away without any need of training -- look at Kroos or Vidal.