Sorry, no hands-on experience here.
But I was thinking of getting one of those - a proper one, not one equipped with cell phone batteries
(those all come in blue plastic cover, btw).
It's ideal for me, too, because I use a push bike to get anywhere dark.
So I read the customer reviews on Amazon - with an eye on whether people use them as constant power source or only to charge devices.
And yes - people do and successfully so.
What a relief, aye!