Umm..winrar and winace are just compression utilities (like winzip) not installers. Compressed files for quicker DL's is always welcome. Its not an uncommon way to distribute mods, cracks, fix's etc.
Easy to use...hardly complicated.
As far as the mod...anyone try it? Played thru original MW but after countless hours of running around it started feeling a bit bland. The game itself ran pretty good for me (none of the problems I read other people having), just felt like the gameplay was missing something