It is best to have a team that can incorporate both man to man and zonal. You must mark man to man on corner kicks or free kicks that are floated into the box. Zonal defending is good if all players understand the game and can see the field. It is good to have many players behind the ball especially if the team you are defending against is very skilled. Space is created when skilled players take on defenders and exploit that space.
Zonal coverage allows backup and gives beaten defenders a chance to recover.
This style of defense is also the present in North America. As a coach of high school girls in the US this is the defense we have been teaching and training them in for at least the past 6 years in our program specifically. The physical demands are not a problem. The outside midfielders are exceptionally capable of these demands. To play this system,it is important for the player to be good defenders first, as well as have a good degree of game insight.