Expedition mode worth using?

FYI Expedition is broken right now, see here

I believe that that bug report is a general issue with the button oriented map controls, not to do with expedition mode. 

Everything is broken now.

You use expedition mode only if you want to record a multiday activity and you won't be able to charge your watch on the way.

You will get a GPS point every hour and you will trade sensors connections and data for longer battery time.
in short: unless you intend to cross Antarctica and you are relying on a GPS computer but you still want a safety track on the watch, I think the expedition mode is kinda useless.
I would rather use the basic GPS and change to UltraTrac in case it is needed (you can do this for any activity in the satellite setting).

I agree. And even using UltraTrac is probably overkill, if you are carrying a powerbank to keep your phone charged. Regardless of the capacity of the powerbank, it will be able to charge your watch several times in addition to your phone. And for an 8 day trip, you'd probably have to charge your watch only once (if even that) if you only record the active portions of the trip, as you wrote.

I've had my Forerunner 965 on a four-day backpacking trip last summer, and I never had to charge it. And it still had about 25 % left afterwards, even though it's amoled and I used the map quite a lot.