Good idea, but the mice are too smart

I bought 2 of these traps because they do not injure or even kill the mice and this is also the case, which was very important to me!
We live on an old farm, because there happens to mice in the shed they are welcome here, but not in the house!
The idea is very good, unfortunately the wrong materials were partly used. Outside is the case perfectly, the grid is stable and closely, but that is not at the entrance / door of the case, there is the grid so großmaschig that the mice just as easily from inside to outside, as move from outside to inside. Slide the grid with the nose high, the smaller force even through the grille. We have seen it! I'll try to replace the grid by a thin, clear plexiglass disk, then it should work.
As a suggestion to the manufacturer!