You told us its not cheating but didn't tell us why it is not cheating.
Because it is not rocket science to know a mouse is better than a controller in every aspect of fps games.
It has also improved a lot since the xim4 model, now called xim apex.
I think it is cheating because I gave some reasons and that also not everybody can use one as their set up might not allow for a mouse and keyboard. Probably a high percentage actually, as most just sit on their sofa and play.