Strahley is right.... you should not need it for a derby cover. BUT if someone else does something foolish, who's to say?? You have a chunk of aluminum, a piece of steel, heat cycles....there is a chemical, galvanic reaction between these two dissimilar metals that occurs. Things happen. I still say for the price of a good hand impact driver you can't go wrong. I just changed primary and was puckered while I removed the derby cover. But they all broke free and no problems. If I had a problem, 5 steps to the tool box and grab the impact driver....
Build your basic tool set first. Then start adding the power tools. Me?? I am a tool-a-holic! I just love buying tools!!!

 

The funny thing is, if you go to Milwaukee web site that exact picture has "impact driver" under it and that's what they call it...

 

Really? not on the page I pulled up

 

Here ya go. Top row middle.......

 

That's a different tool then the one in the picture I posted. The tools with a fixed anvil ( the part you put a socket on ) are called impact wrenches. The one you are referring to has various bits that are inserted into it. Those are called impact drivers, which I guess came from the early battery drills being referred to as a "drill/drivers"?
So I guess you could call the hand held hammer unit an "impact driver" and the other an "electric impact driver"?

Mine has Impact Wrench stamped on the label.