If you are going to take the ballancer off after the impact is the right tool to get the bolt loose/off as well. You will need a puller to take the ballancer off.
Lots of choices I would say just think for a second.
In car? Put car in gear.
Not in car? Use screwdriver through the flexplate or flywheel.
No flexplate or flywheel? Thread a couple bolts into the back of the crank and stick a bar between them.
Oil pan off? Stick a bar between the crank and block (not on a bearing surface!).
Yes you can use an impact if you have one. I have a cheap enough impact that if a fastener is too tight I will have to break it loose by hand. It did work great for getting that alternator nut off, though.