Runesika,
Maybe I'm too cautious, but I have in my possession 50 plus year old engines with broken bolts and screws in them the handiwork of previous would be mechanics. I have had an Impact Driver for 30 plus years but rarely used it, as I have had a policy of replacing the cross-headed screws with Allen screws & where possible Allen bolts for hexagonal-headed stuff.
Usually this has solved the problem of freeing off stuff, with an impact driver you do have to watch that you use the right length of screw bit, to avoid marking the alloy on engine cases, some places of course you can't use them at all, because of lack of space , hence the advantage of Allen keys in tight spots.
Cheers
JBW