How is it a matter of opinion? He has proven to be lethal in Europe as well as domestically, being one of the best LB's in the world and arguably Brazil's best LB both defensively and going forward.
Every top successful footballing club has exceptional wing backs. Having him and Alonso would improve us tremendously, and would be a definite upgrade on Alonso.
We have the money to get a goal scorer as well as improve other areas. What frustrates me is that instead of achieving these targets, we are too busy buying youngsters titled as 'the next messi' or 'the next ronaldo' yet won't ever reach their potential, loan out to Vitesse, then never to be heard of again.