Just wanted to compare those 2 great DeWalt tools. To summarize this review: I was impressed with the DCF921, which is very powerful for the compact size. The reason I got the bigger one, is because it came with 2 free 1.7 ah batteries, and when you have car sitting outside, you get 1 or 2 nuts that the smaller impact would take too long to loosen up, and too much vibration destroys your sockets or adapters (the female part grinds off a little each time). But if you are on a budget, or don't like to collect tools just for fun, you can get away to tackle most small vehicle wheel rotations with the DCF921. Great small tool that you can hang on your belt and walk around.

DCF921 https://www.dewalt.com/product/dcf921...

DCF891 https://www.dewalt.com/product/dcf891...

PowerStack Battery DCBP520 https://www.dewalt.com/product/dcbp52...