Having now had both Zero and Duo side by side for a month, I can say that they are both good. The Duo fares better for lighter roasts, the Zero seems to be more suitable for medium/dark and darker roasts - this is according to my taste, which is subjective and what I like is not necessarily what someone else does.
The only way I can describe the difference is that the Duo produces a crispier cup (sorry, very poor adjective for this!) whereas the Zero muddles the flavours more. Saying all of that, the difference, for me at least, is subtle. I wouldn’t be able to tell the difference if they were not side by side.
Concrete examples to illustrate this:
I used to say I couldn’t tell the difference between the Zero and the Duo - that was because I was using the Zero at home, and went to Dave’s home, brought my own beans and had coffee from the Duo there. It felt they tasted the same, but now I have them both here in my home, I can tell there’s a subtle difference between the two.
Also, I remember going to Dave and sharing the coffee I was drinking at home with him (a very light roast, of course). Dave made a comment that my coffee potentially had a roast defect, or not roasted well - whereas I really enjoyed that particular coffee! I then drank some of the coffee Dave was drinking and it was a very different coffee, and tasty too. But it goes to show how subjective taste is.
