The mesh really isn't much better then running open turbo. Sure it keeps large items from getting sucked in, but it still allows dirt, small rocks, and other hard, very bad shit to get in the housing and eventually it will cake up, and damage the turbo.

Using a screen will not screw up the intake ability of the turbo. The turbo is pulling air from the outside at a good velocity on it's own, having something like a filter or screen will impare this only slightly.