If you were looking at Bushmaster, you are going to be shocked at the price of the KAC unit. That said, all my two stage triggers are KAC, especially my M16 trigger. As easy to install as DevL said. Pull the KAC trigger and you will know what all that money went towards. IMHO, the only caveats that can disqualify the KAC, money aside, is the SHTF factor (set screws, and is a subject of much debate (I'll call virtual bull$hit), and those that prefer single stage.
As far as the Bushy trigger, don't waste your money, make your last choice the RRA trigger - a good value for the money and a decent trigger - and go up from there.
P.S. If you get the KAC, and decide you don't like it, I'll buy it from you at a used price [;)]
Edited to say: That last line was a waste of typing cause it ain't gonna happen!