Exactly the reason I haven't bought a Garmin device. Though it runs linux you have to either be a mac or Windows user to use its software and that runs in a browser plugin.
Hey ho, money in my pocket.
Regrettably, there are no satnav devices that I could find when I was researching what to buy that allow updating by a Linux OS; they all need Windows or Mac.
My only available Windows was XP so in spite of the fact that it is out of support I still use it for about 3 minutes a month to update the TomTom. If the XP VM should get infected in spite of running a firewall and Avast AV, I shall just reinstate a clean snapshot of the VM and I am back to a good version again.