I like the looks of that one.
I have one very tiny one that is left over from my old dumbphone. It was barely bigger than the single AA cell it used, and I kept in in my brief case at all times. I no longer have the phone or the briefcase, and I doubt it would be powerful enough for new devices.
I built one from a kit that used two AA cells, and it worked for about a week. I can solder, but not exceptionally well
And I got a rechargable recharger (weird to my mind) in a bundle with my new smartphone. My wife uses that one with her phone.
I also have a portable solar charger that charges four AA cells. I might modify it into a USB charger with the parts from the above mentioned kit.
Sorry for the tangent. As you were.