JB,
I have a mikita spline drive and I use it often. Driving ground rods is a sinch. $10. attachment set it on hammer only and away you go. Also use it as a jackhammer from time to time. Cot in boxes in brick, block or break up concrete around pole/posts.
I like the spline drive as the bits are less expensive and readly available. So far I have not used it for anyhting larger than 2 1/2" core bit. I am presently bidding a job that will require a 3" conduit though concrete floor. Hope this helps!
Phil
