Steve, I am not aware of ant 'combo' drill / impact drivers being sold. I think you have a hammer drill. Let me explain the difference:
A hammer drill is used for drilling in masonry. Almost everyone sells combo drill/ hammer drill models. In a hammer drill, the impacts are directed forward, into the work.
An impact driver may sound sort of similar, but the impacts are directed in the direction of the rotation. You can even get the impacts when backing out of the work. You absolutely will never feel the tool want to 'tear your arm off.'
In appearance, one of the main ways to tell them apart is that an impact driver almost never has a standard chuck; it has a little collar that you lift, to insert a bit with a 1/4" hex shank. It will not accept anything else.
I have not destroyed any bits, and twisting screw heads off has not been a problem at all.
I think you have a different tool.
