They are. I have a 15000 mAh unit; two, 2.4 ampere outputs. Wouldn't be without it, can't really, at least unless the companies making the cellphones stop putting too-small batteries in them. last weekend I drove five hours, during about 3 of which we were either completely out of contact or only in distant contact with a cell tower (Montana... lots and lots of empty space.) When we left the city, my phone was at 25%. I kept the phone (a Galaxy Note III with an aftermarket "big" battery that's good for about 48 hours here, where we're within about 4 miles of a cell tower) plugged into the external unit for the entire trip, and when we got home, the phone was at 100% and the external unit at 45%, which allowed for both charging it and running it.
Really, won't even consider being without that external unit. As for a pager... no. Just no.