went this very route in august now sitting top of the douro valley all systems fine , jan has an unlimited 3 contract on her phone at home (rural rutland ) she gets 3bar 3g signal the cube powered up and gave 4bar 4g same location , i tried to get a 12v feed from 3 worse than useless rang huawei said none available but tech guy said no reason one wouldn’t work after advice from several on here i cobbled together two leads that work just fine ,
connection has worked fine and signal strength stable wherever i have been through france & spain cube is in middle of van and can get connection outside from10 mts away & the kids love the alexa facility
ps i took out the 12 month contract at the time it was £20 for 24 months £25 for 12 months & because i am an existing customer & told him i was also looking at a vodaphone deal the upfront cost was wiped , i only took the 12 month deal because jan’s unlimited sim in her phone is on a loyalty deal she only pays £18 55 and well put that in the cube end of the year,
we have used netflix & now tv through the cube at home and around the uk though a chromecast with great success not tried it abroad yet but will soon