Hannah Dhonauwrote a review of Goal Zero Flip 20 Recharger on February 4, 2019
Familiarity: I've used it several times
The Flip 20 is a light-enough super-small and powerful cache battery to bring along. I use this primarily when bikepacking, to keep my phone charged for tunes and navigation. I'm able to charge my phone 1-2 times off the Flip, which recharges itself fairly quickly.
My one small gripe with the Flip is that its own USB power inlet feels like it may not last the long haul/does limit the positions you can charge it. Overall, pretty pleased and eager to keep using this tiny bub in remote spaces.