OK, I'll bite! it is the season of goodwill ! My 2 pence
If you already own an InReach device, you don't need the 700i.
If you have. Montana 600, you'll be fine so no need to spend unless you want to.
Some of the avantages of the 700 include:
16GB of internal memory and up to 15000 map segments.
10000 user waypoints
TRACKS 250
NAVIGATION TRACK LOG 20000 points, 250 saved gpx tracks.
NAVIGATION ROUTES 250, 250 points per route; 50 points auto routing
Rinex logging
GPS, Glonass and Galileo
Meets MIL-STD 810 for thermal, shock, water and vibration.
And as far as power, 18hours in GPS mode or 330! in Expedition mode.
And more!
So IMHO, without any doubt the '700' is a better and faster unit than the 600; the question has to be : will you actually make use of those extra facilities?
Only you knows that answer.