Logitech does have brilliant hardware engineers. However their software "engineers" are not very bright.
I have used their hardware in OS X since it arrived. The story is always the same:
Major updates cause their software to cease functioning as designed. I will also add that it takes them months to update the software to restore full functionality to the device(s) you may be using.
This is not an attempt to be helpful, just stating a fact that is never going to change. They appear to not take advantage of Apples Beta periods to work on their drivers. They wait until a release version to BEGIN working on new drivers.