I don't know how their cordless impacts are, but I have an electric impact that I bought from Harbor Freight about 10 years ago and it is still as good as it was the day I bought it. I haven't got hold of anything yet it wouldn't break loose.
I've seen a few brands that did well. I know the Snap-on works well, and the other one I've used is a Milwaukee (I think).
They are not designed for professional use. If you want one for just occasional use (i.e. changing tires at the track, winter/summer changovers, etc.) look at JC whitney- they sell a 12V impact gun that does the trick okay from the cigarette lighter (and you can buy 10 of them for the price of a good rechargeable).
craftsman makes a good cheap 19.2v set and they work good for the money.
I have a bosch 18v with alot more power at five times the cost. The bosch is designed to take a two story drop and is twice as heavy, but if your not using it every day the craftsman is a great deal.