The copper/nickel mix is apparently more future proof. I read that the pure copper eventually hardens? and can go funny at joints. However having seen first hand 90yr old copper work that still is fine I don't believe it, and the copper is easier to work
I have an automec former, the vice mount job, only did a couple joints with it which turned out crap and was hard work but it seems a nice bit of kit and I reckon time you did it all yourself you'd have paid for the tool.