Huh? I don't know of any Logitech mice that have issues with OS X, especially on the mid-end models like the G400/MX518. You don't even need to install the drivers, just plug it in and go... all buttons will be recognized and sensitivity adjustments work fine. I've used Logitech mice/trackballs with Macs for almost a decade now without a single problem. USB mice are nearly universal these days and only a handful exhibit problems with OS X.
The only "problem" I've heard people speak of is Mac OS X's mouse acceleration curve, which is independent of the mouse being used. I say "problem" because I bounce between Mac OS and Windows constantly and can't tell a difference... they feel identical to me, so that "problem" is subjective at best and if your friend has been using Macs for any amount of time at all, he's probably accustomed to the curve.