If my memory serves me right, there was some discussion about lag back in 2002 or so. However, reading the reviews for Logitech Freedom 2.4 tells there wasn't any.
The reviews also say that the three AA batteries last for 50 hours just as Logitech had promised. Not too bad if you only play on weekends, or a couple of hours daily.
Even the development cost should be no issue, the same radio technology is used for mice and keyboards.
Maybe it's the lag anyway. Hard core players can sense microseconds... There's been talk about wireless keyboards and mice not being the best option for fast paced shooters, too.
Someone in our squad might have had a Freedom.