>>1001320most are garbage but there are some good ones out there.
the real question is more about where the break even point to a normal power bank is.
unless you actually me a combined product like in the picture you posted they are 99% absolute garbage. basicly free merchandise multitool level of trash.
i tend to favor power banks
381g Anker PowerCore 20100mAh
+ guaranteed charge phone 6 or more times
+ works in any weather & time
+ full power output
+ small dense object
+ back to full charge in one stop
- slow loss of charge over months
- dead weight once empty
vs
354g PowerPort Solar Lite 15W
+ infinite energy
+ independent
+ produces power after long storage
- limited output
- depending on weather and time
- needs to somewhat face the sun
- somewhat bulky shape
- might not meet minimum power to charge stuff without reservoir
