The thing is, if you need a breaker bar to shift it, it's touch and go whether a cheapish impact wrench will help. They are great for spinning fasteners off once they are loosened, and where there is room to get it in place but for loosening off bolts you really need a breaker bar IMHO.
Something like a suspension bolt that has been there for years is better off loosened by hand, IMHO, because
a) An impact wrench might well not shift it anyway.
b) An impact wrench might well be too bulky to get anywhere near it.
c) By hand you can feel what's happening and are less likely to muller it IMHO.
d) By the time you get the impact wrench, air line, compressor, etc. out, you'll have done the job anyway.
If the above is your main application you'd be better off with an electric impact wrench than a compressor and all the paraphernalia anyway. If you have a compressor for other reasons, adding a £20 impact wrench is a no brainer over buying a £100+ electric one, however.