Today Nov.2/2018 with a difficulty around 42m the z9 mini would mine about 9 ZCash in a year at 360 watts. Back before ASICs took over, at around 10m difficulty, ONE 1080TI would mine 2.4 Zcash at 180 watts.
Soon the z9mini will be less efficient than a GPU per coin. With the big spikes of difficulty, a ASIC company is most likely getting a new model online. Sadly difficulty is going to keep shooting up, the arms race has begun.
This is why GPU mining is so much better. The hardware does not become obsolete in 3 months, its closer to 3 years for GPUs. Whats the point with ASICs if you are racing to pay off your miners, only to be stuck with something that loses you money 3-6 months later. Now you have to spend most of the money you just made back on miners or your done mining. Repeat every 3-6 months, soon the miners begin to become a huge money sink.