BrewLiam the Duo wins hand down in the quality department for sure, and not just the sound.
In the UK the pricing of the Duo makes it very competitive. The following is not to speak to you point, which I agree with, more about general musings….
When people choose a grinder there are few factors they typically weigh up: in-cup-result, aethetics, footprint, workflow, engineering (if they have enough knowledge) and of course price.
Just on the latter alone however, a single burr set Duo can be landed here in Australia for around the AU$1,400 mark including shipping and import charges (the same grinder will set you back around AU$2,000 if you buy locally).
The DF64 Gen 2 can be landed here for AU643. Add $50 to upgrade to DLC burrs and it is a very attractive option for people who want to save a bob or two. I expect them to be around the AU$750 mark when they are made available locally.
I really like my Duo for sure, but looking at the choice (here in Austalia at least) for a new buyer wondering which grinder to buy, both the Gen 2 with DLC burrs and the Duo are both going to produce a very nice in-the-cup result but the Gen 2 can do do for less than half the price.