Worth buying a fenix 6s watch in the US if i live in Europe?

You can download and install OSM maps for any region. Details at https://www.dcrainmaker.com/2019/08/how-to-installing-free-maps-on-your-garmin-fenix-5-plus-forerunner-945-or-marq-series-watch.html

It is the same base map data. What you won't get if buying in the US is the Garmin popularity routing for Europe.

It depends on the price difference. I chose not to (live in Sweden) due to the maps installed. There is no way you will get the Garmin Europe maps on a US device unless you buy them from Garmin. As said by mcalista there are OSM alternatives but in my opinion that is not an replacement, it's an optional choice that may work in some situations.

In the end I bought mine from UK with a discount, compared to US prices it was about the same.

If you want to run while in the US - then maybe buy it in the US and buy the EU Garmin Charts for when you get back (Remember you get a 10% off voucher when you register your watch - online purchase is quick and relatively painless)

But then you might run into warranty issues when you get back. I don' t know how Garmin handles international warranty for watches. 

So my recommendation - try and find one in DK - or UK (eBay?) with EU charts and warranty.

But if you want both sets of charts on the watch - I would get the 6S Pro that has 32GB of flash memory....

/k

Please check the warranty! As far as I know, you only have one year in the US. As quite a high number of watches have to be returned, this can be expensive in the second year.