@t3p3tony, I am still at the waiting stage for the arrival of my killerbee, otherwise I would test this out myself.
My main interest lies in the bluetooth connection, because if this works it will be a much cheaper alternative to the PanelDue or a pendant, at a cost of around £5 (plus a couple of connectors).
The app itself is free, and offers way more control and features, and can be used on an Android smartphone or tablet. It can control the cnc both with up/down/left/right buttons, and also with a really useful touchpad control. My limit of understanding is that the app is 'grbl1.1-compliant'. I'm not sure whether the Duet meets this requiement.
As I said earlier, I have successfully used it on my CNC3018 for a while and find it really easy to use.