FWIW, I think an air impact wrench is a better choice if you're not going to be using it on a daily/weekly basis. The battery(ies) in the battery operated tool will degrade, whether Ni-Cd or LI. If the tool is only going to used monthly or few times per year, an air tool will likely last decades whereas the battery operated tool will need a new battery (batteries?) long before that. Don't get me wrong, I've been extremely tempted by those Milwaukee units but the realist in me sees dead batteries and a PITA at some point in the future.
On the breaker bar front, I had a 1/2" breaker bar with a 5 foot extension (and I'm 225 lbs.) and I couldn't get the axle nut off of my Subaru Legacy. Took it to a shop and they busted out the big, two-handed, impact gun and got it loose (after attempting to use their breaker bar whilst doubting my ability to use on properly). Once off, they torqued it back to spec, I drove it home, and finished replacing the half-shaft (using my breaker bar to remove the axle nut this time). The next time I needed to replace a half-shaft I went to Harbor Freight beforehand and picked up their 900+ lb/ft air impact wrench and boy was I glad I did. Zipped that (and many more) axle nuts right off. It was right around $90 IIRC.
CN: air tools better for light usage, big (strong) air impact good for stuck nuts
-Brian