A friend of mine has a milwaukee 1/2" cordless impact. It's pretty good. It's great in the junkyard or on the side of the road when something is broken. Maybe changing a tire in the shop when I don't wanna run an air hose. I still way prefer my 1/2" pneumatic, though. It's lighter, more powerful, smaller to fit in tight spots, and I can run it 100% duty cycle going nuts ripping things apart. If you do that on an electric impact you'll overheat it.
Even when I do rally service for the race car, I drag my generator and 30 gal compressor along with me to the service park.
Electric impacts are a long way for replacing pneumatic tools for me. Once you have a good pneumatic rattle gun in your hand, you're gonna be hard pressed to let it go.