Make sure you're comparing the exact same software
. We sell MSTZ for much less than you're "US from Furuno" price
- so the difference is even more than what you think it is.
There are 2 products - one that is a stand alone software navigation
product and one that is meant to integrate into NavNet3D. In addition, the US version comes with US charts
and the UK version comes with UK charts. The UK charts have a higher price than the generally free/low cost US NOAA charts.
It might also be that there is something additional being charged. But just make sure you're comparing the same things.