There are at least two part numbers for the 1/4" impact driver. The one I bought claimed something like 1500 in-lbs of torque. That's an exaggeration. I know that impact tools are rated optimistically with a "let it sit all day on the fastener with the voltage from a fresh battery" approach. And then round up. But there is no way this tool will torque or loosen a fastener with even 20% of the rating on the box.
You did get that 1500
in-lbs is 125
ft-lbs, right?
I have both of these tools (the 1/2 impact wrench, and the hex impact driver), and I don't doubt either of them achieving their rated torque. With a socket adapter, I have used the hex driver to remove lugnuts that were properly torqued to the car. These were not lugnuts with any rust, or ones that had been unloosened for 2-3years, but still, it was a respectable accomplishment for a tool not really meant for that kind of use.
The impact wrench, I believe, is rated for 200 ft-lbs. That is setting the bar pretty low, but it achieves that easily, if your battery has better than half charge.
If you're on the bottom half of the battery, I would not attempt lugnuts. I probably would not attempt fasteners bigger than 3/8". Performance of these tools falls off rapidly after the first half or so of the battery is spent. The hex driver will still drive screws, and the impact wrench will still handle small fasteners, but you best charge or change batts before attempting anything serious.
A LI battery really wakes these tools up.